Effects of ketoconazole on the pharmacokinetics of doramectin in rabbits

Effects of ketoconazole on the pharmacokinetics of doramectin in rabbits | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Effects of ketoconazole on the pharmacokinetics of doramectin in rabbits Ahmed E. A. Mostafa This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7880017/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract This study aimed to investigate the influence of ketoconazole-mediated inhibition of P-glycoprotein (P-gp) on the pharmacokinetics of doramectin (DRM) administered orally and subcutaneously (SC) in rabbits. Twenty New Zealand rabbits were allocated into four groups (n = 5) and received DRM either orally or SC (0.2 mg/kg) alone or co-administered with ketoconazole (10 mg/kg PO, three doses at 12-hour intervals). Plasma, fecal, and urine samples were collected over 30 days to assess DRM concentrations. No significant differences were observed in the pharmacokinetic parameters of DRM between oral and SC administrations when given alone. However, co-administration with ketoconazole significantly altered DRM pharmacokinetics. The area under the plasma concentration–time curve (AUC₀–∞) was higher (p < 0.05) after oral DRM/ketoconazole treatment compared with oral DRM alone. Time to reach Cmax was shorter (p < 0.05), while elimination half-life (T1/2) and mean residence time (MRT) were prolonged (p < 0.05) in the presence of ketoconazole. Additionally, fecal DRM concentrations were reduced when DRM was administered with ketoconazole, either orally or SC, compared with DRM alone.Specifically, co-administration increased DRM AUC₀–∞ from 302.1 to 565.8 ng·day/mL (p = 0.003) and prolonged the elimination half-life from 42.5 ± 5.8 to 66.9 ± 6.1 h (p < 0.01). These findings indicate a clinically relevant pharmacokinetic interaction, likely due to inhibition of P-gp-mediated intestinal secretion, which may alter DRM’s antiparasitic efficacy and warrants caution when co-administering antifungal azoles with macrocyclic lactones. All animal procedures in this study were approved by the Research Ethics Committee of the Faculty of Veterinary Medicine, Delta University (Approval No. FPDU15/2025) and conducted in accordance with the ARRIVE guidelines. The findings provide practical insights for veterinary pharmacologists and rabbit producers regarding the safe co-administration of Doramectin and Ketoconazole, emphasizing potential pharmacokinetic interactions, appropriate withdrawal periods, and strict adherence to animal welfare and food safety regulations. Health sciences/Diseases Biological sciences/Drug discovery Health sciences/Medical research Biological sciences/Microbiology Doramectin Ketoconazole Pharmacokinetics P-glycoprotein (P-gp) inhibition Drug–drug interaction Rabbits 1. INTRODUCTION Doramectin (DRM), a derivative of avermectins, is a broad-spectrum antiparasitic agent belonging to the family of 16-membered macrocyclic lactones. DRM was originally obtained through chemical modification of ivermectin, which is produced by the fermentation of Streptomyces avermitilis (Shoop et al., 1995 ). It exhibits potent activity against a wide range of endo- and ectoparasites in domestic animals, particularly nematodes and arthropods (Shoop et al., 1996 ). The mechanism of action of DRM involves binding to γ-aminobutyric acid (GABA)- and glutamate-gated chloride channels in nerve and muscle cells of parasites, resulting in hyperpolarization, paralysis, and eventual death of the parasite (Arena et al., 1995 ; Martin et al., 2002 ). Like other macrocyclic lactones, DRM shows a high safety margin in mammals due to limited access of the drug to the central nervous system (CNS), which is attributed to the efficient P-glycoprotein (P-gp)-mediated efflux across the blood–brain barrier (Schinkel, 1997 ). P-gp, encoded by the multidrug resistance (MDR1) gene, is a member of the ATP-binding cassette (ABC) transporter family and plays a major role in drug efflux and detoxification (Sharom, 2011 ). It is widely distributed in the apical membranes of intestinal epithelial cells, biliary canaliculi, renal proximal tubular cells, and endothelial cells of the blood–brain barrier (Thiebaut et al., 1987 ; Edwards et al., 2005 ). By pumping xenobiotics and therapeutic agents out of cells, P-gp limits intestinal absorption, reduces drug bioavailability, and restricts tissue distribution (Schinkel et al., 1994 ; Melaine et al., 2002 ). Therefore, inhibition of P-gp can significantly alter the pharmacokinetic (PK) profiles of P-gp substrate drugs, potentially leading to higher systemic exposure and prolonged elimination. Ketoconazole (KTZ), a widely used imidazole antifungal drug, is a potent inhibitor of cytochrome P450 (CYP3A4) enzymes as well as P-gp (Tanigawara et al., 1992 ; Kim et al., 1999 ). KTZ is frequently used in veterinary medicine to treat fungal infections in small animals and has been reported to increase plasma concentrations of P-gp substrate drugs by inhibiting their intestinal efflux and hepatic metabolism (Liu et al., 2010 ; Zhang et al., 2008 ). Therefore, its co-administration with macrocyclic lactones such as DRM could potentially modify the disposition and bioavailability of these antiparasitic agents. To date, limited information is available regarding the effects of P-gp inhibitors on the pharmacokinetics of DRM in nonruminant species such as rabbits. The rabbit represents a suitable model for pharmacokinetic studies, as it allows serial sampling of plasma, urine, and feces following both oral and subcutaneous (SC) administration (Hedaya et al., 2017 ). Accordingly, the present study was designed to investigate the influence of ketoconazole-mediated inhibition of P-glycoprotein (P-gp) on the pharmacokinetic behavior of doramectin administered orally and subcutaneously in rabbits. Since P-gp functions as an efflux transporter, we hypothesized that inhibition of this transporter by ketoconazole would result in decreased intestinal excretion and increased systemic exposure of doramectin, potentially altering its antiparasitic efficacy. 2. MATERIALs AND METHOD 2.1 Chemicals An injectable formulation of doramectin (Dectomax®, 10 mg/ml), produced by Zoetis Egypt, was used in this study. The solution was diluted with propylene glycol (Sigma-Aldrich Co., St. Louis, MO, USA) to obtain a concentration of 1 mg/ml before administration. The doramectin reference standard was obtained from Sigma-Aldrich Co. (St. Louis, MO, USA). Ketoconazole tablets (Nizoral®, 200 mg/tablet), manufactured by Janssen-Cilag Egypt, were crushed and freshly suspended in distilled water containing 0.5% carboxymethylcellulose (CMC) before oral administration at a dose of 10 mg/kg. High-performance liquid chromatography (HPLC) grade methanol, acetonitrile, ethyl acetate, hexane, acetic acid, and triethylamine were obtained from Fisher Scientific (Loughborough, UK). Aqueous ammonia was supplied by Merck KGaA (Darmstadt, Germany). Water used in all analytical procedures was purified through a Milli-Q system (Waters Corp., Milford, MA, USA). All chemicals and solvents used were of analytical grade. 2.2 Animals Ten healthy adult New Zealand white rabbits (2.5–3.0 kg) were used in this study. Animals were randomly assigned to two groups (n=5 per group). Group I received doramectin (0.3 mg/kg, IM) alone, while Group II received ketoconazole (10 mg/kg, orally for 5 days) followed by doramectin (0.3 mg/kg, IM) on day 5. Blood samples were collected from the marginal ear vein at 0, 0.5, 1, 2, 4, 8, 12, 24, 48, 72, 120, and 168 hours post-dose. Plasma doramectin concentrations were quantified using a validated HPLC method.The animals were obtained from the Experimental Animal Unit, Faculty of Agriculture, Mansoura University, Egypt. Rabbits were housed individually in stainless-steel metabolic cages designed for the separate collection of urine and fecal samples (Harvard Apparatus, MA, USA). Environmental conditions were controlled and maintained at a temperature of 20–22°C, relative humidity of 40%–70%, and a 12 h light/dark cycle. Animals were fed a commercial pelleted rabbit diet (El-Nasr Feed Company, Cairo, Egypt) and provided free access to clean tap water throughout the experiment. Prior to the start of the trial, all rabbits underwent a two-week acclimatization period during which they received no antimicrobial or antiparasitic treatments. 2.3 Experimental Design The twenty (20) rabbits were randomly assigned into four groups (n = 5 per group). Each group received doramectin (DRM, 0.2 mg/kg) either alone or in combination with ketoconazole (KTZ, 10 mg/kg) according to the following treatment schedule: Group 1 (DRM-Oral): Received doramectin orally (0.2 mg/kg) as a single dose. Group 2 (DRM + KTZ-Oral): Received ketoconazole orally (10 mg/kg) three times at 12-hour intervals, and the first dose of ketoconazole was administered 30 minutes before doramectin oral administration (0.2 mg/kg). Group 3 (DRM-SC): Received doramectin subcutaneously (0.2 mg/kg) as a single dose. Group 4 (DRM + KTZ-SC): Received ketoconazole orally (10 mg/kg) three times at 12-hour intervals, and the first dose was administered 30 minutes before doramectin subcutaneous injection (0.2 mg/kg). The selected dose of ketoconazole was based on previous reports describing its potent inhibitory effect on P-glycoprotein and cytochrome P450 (CYP3A4) enzymes in rabbits and other species (Tanigawara et al., 1992; Liu et al., 2010). Doramectin doses were chosen according to therapeutic levels used in veterinary medicine (Shoop et al., 1996). All animals were observed throughout the experimental period for any clinical signs of adverse reactions. Blood, urine, and fecal samples were collected according to the schedule described in Section 2.4. 2.4 Blood Sampling Blood samples (2 ml each) were collected from the marginal ear vein of all rabbits at predetermined time points: 0 (prior to doramectin administration), 15 and 30 minutes, and 1, 2, 3, 6, 12, 24, and 36 hours, as well as 2, 3, 4, 5, 7, 9, 12, 15, 20, 25, and 30 days following doramectin administration. Samples were collected in heparinized tubes containing ethylenediaminetetraacetic acid (EDTA) as an anticoagulant and immediately centrifuged at 3,000 × g for 10 minutes to separate plasma. The obtained plasma was carefully transferred into labeled Eppendorf tubes and stored at −20°C until quantitative analysis of doramectin concentrations. 2.5 Collection of feces and urine samples Fecal and urine samples were collected daily from all rabbits throughout the experimental period. Samples were accumulated over 24-hour intervals at time 0 (before doramectin administration) and at 1, 2, 3, 4, 5, 7, 9, 12, 15, 20, 25, and 30 days following doramectin administration. Each sample was placed in pre-labeled sterile containers and immediately stored at −20°C until analysis of doramectin concentrations. Care was taken to prevent contamination between samples and to ensure complete separation of feces and urine in the metabolic cages.2.7. High-Performance Liquid Chromatography (HPLC) 2.6 Analysis of DRM in plasma and urine samples For the preparation of plasma and urine samples, a 0.5 ml aliquot of each plasma or urine sample was transferred into a clean microcentrifuge tube. Subsequently, 250 µl of ethyl acetate was added and mixed with 250 µl of acetonitrile to precipitate proteins and improve extraction efficiency. The mixture was vortexed for 1 min and then centrifuged at 4,000 × g for 5 min. The upper organic layer was collected and transferred to a new tube. The extraction step was repeated using 250 µl ethyl acetate to ensure maximum recovery of doramectin. The combined organic layers were evaporated to dryness under a gentle nitrogen stream at 40°C. The residue was reconstituted with 0.5 ml of methanol and vortexed for 30 s. Finally, 50 µl of the reconstituted sample was injected into the HPLC system for analysis. Urine samples were not subjected to hydrolysis to release DRM from conjugates because most of the administered dose is excreted unchanged in rabbits (Canga et al., 2009). Doramectin concentrations in plasma and urine samples were determined using a validated HPLC method adapted from Zhao et al., (2005). The HPLC system consisted of an Agilent Series 1200 quaternary gradient pump, Series 1200 autosampler, and Series 1200 UV–VIS detector set at 245 nm, controlled by HPLC 2D ChemStation software (Hewlett-Packard, Les Ulis, France). Separation was performed on a Phenomenex C18 column (5 µm, 250 mm × 4.6 mm). The mobile phase consisted of methanol:water (90:10 v/v), filtered and degassed prior to use. The flow rate was set at 1 ml/min, and the injection volume was 50 µl. The retention time of doramectin was approximately 11.2 min. The method was revalidated according to the European Medicines Agency (EMA, 2009) bioanalytical guidelines. Linearity was observed over the concentration range 0.25–1,000 ng/ml, with an R² > 0.99. The lower limit of detection (LOD) and lower limit of quantification (LOQ) were 0.1 ng/ml and 0.25 ng/ml, respectively. Table 1. Validation parameters of the HPLC method for doramectin in plasma and urine samples. Data are presented as mean ± SEM Matrix Average recovery (%) Intra-day RSD (%) Inter-day RSD (%) LOD (ng/ml) LOQ (ng/ml) Plasma 102.18 ± 2.26 2.10 3.67 0.1 0.25 Urine 99.97 ± 0.93 2.98 2.88 0.1 0.25 Note: -Intra-day and inter-day RSD were calculated using six replicates at 10 ng/ml. -Average recovery was determined using spiked concentrations ranging from 0.25–1,000 ng/ml in triplicate. 2.7 Analysis of DRM in fecal samples 2.7.1 Preparation of standards and fecal samples A stock solution of doramectin (DRM) at a concentration of 1 mg/ml was prepared by dissolving 100 mg of DRM standard in 100 ml of acetonitrile (HPLC grade). Working standard solutions were then prepared by serial dilution of the stock solution with acetonitrile to obtain final concentrations of 2.5, 25, 100, 500, 1,000, 2,500, and 5,000 ng/ml. For calibration curve construction, these DRM working solutions were added to blank rabbit fecal samples to prepare fortified fecal standards with final concentrations of 2.5, 25, 100, 500, 1,000, 2,500, and 5,000 ng/g. The mixtures were vortexed for 20 seconds and allowed to stand for 10 minutes to ensure complete adsorption of DRM to the fecal matrix. The extraction of DRM from fecal samples was carried out according to the method described by Jiang et al. (2008) with minor modifications. Briefly, 1 g of fecal sample was mixed with 2 ml of acetonitrile and vortexed for 2 min. The mixture was centrifuged at 4,000 × g for 10 min, and the supernatant was collected. The derivatization of DRM was then performed by sequentially adding equal volumes of N-methylimidazole-acetonitrile (1:1, v/v) and trifluoroacetic anhydride-acetonitrile (1:2, v/v) to the supernatant. The derivatized samples were mixed and left at room temperature for 15 minutes prior to HPLC analysis. Finally, 100 µl of each derivatized sample was injected into the HPLC system. 2.7.2 Chromatographic condition The quantitative analysis of doramectin in fecal samples was performed using the Agilent Series 1200 HPLC system equipped with a quaternary gradient pump, autosampler, fluorescence detector, and HPLC 2D ChemStation software (Hewlett-Packard, Les Ulis, France). Separation was achieved on an Inertsil ODS C18 column (4.6 mm × 250 mm, 5 µm). The fluorescence detector was set at an excitation wavelength of 365 nm and an emission wavelength of 475 nm. Preliminary UV detection trials were conducted, but fluorescence detection was selected due to its superior sensitivity and specificity and the absence of interfering peaks from fecal components. The mobile phase consisted of methanol:water (90:10, v/v), filtered and degassed before use. The flow rate was 1.5 ml/min, the column temperature was maintained at 30°C, and the retention time for doramectin was approximately 6.8 minutes. The method was validated according to EMA (2009) guidelines. The calibration curve exhibited linearity over the range of 2.5–5,000 ng/g, with the regression equation y = 318.58x − 0.0838 and a correlation coefficient (R²) greater than 0.99. The lower limits of detection (LOD) and quantification (LOQ) were 1 ng/g and 2.5 ng/g, respectively. Table 2. Validation parameters of the HPLC method for doramectin in fecal samples. Data are presented as mean ± SEM Matrix Average recovery (%) Intra-day RSD (%) Inter-day RSD (%) LOD (ng/g) LOQ (ng/g) Feces 94.92 ± 3.47 0.59 1.19 1 2.5 Note: - Intra-day and inter-day RSD were calculated using six replicates at 25 ng/g. - Average recovery was determined using spiked concentrations ranging from 2.5–5,000 ng/g in triplicate analysis. 2.8 Pharmacokinetic Analysis The pharmacokinetic parameters of doramectin (DRM) were calculated individually for each rabbit using plasma concentration–time data obtained after single and combined administration with ketoconazole. Analysis was performed by applying a non-compartmental model using WinNonlin software version 4.1 (Pharsight Corporation, Mountain View, CA, USA), following the approach described by Gokbulut et al. (2010). The peak plasma concentration (Cmax) and the time to reach Cmax (Tmax) were directly determined from the observed concentration–time profiles. The first-order elimination rate constant (λz) was obtained from the slope of the terminal log-linear phase of the plasma concentration–time curve. The elimination half-life (T1/2λz) was calculated using the equation T1/2λz = 0.693 / λz. The area under the plasma concentration–time curve from time zero to infinity (AUC₀–∞) was calculated using the linear–log trapezoidal method. The mean residence time (MRT) and area under the first moment curve (AUMC) were also estimated to describe the extent and persistence of systemic exposure. Pharmacokinetic parameters were expressed as mean ± standard error of the mean (SEM) for each experimental group, and comparative evaluation between doramectin alone and doramectin–ketoconazole co-administration was conducted to assess possible pharmacokinetic interactions. 2. 9 Euthanasia Protocol Rabbits were humanely euthanized at the end of the experimental period using isoflurane inhalation (5% concentration in oxygen) administered in a sealed induction chamber until complete loss of righting reflex and deep anesthesia were confirmed. To ensure death, cervical dislocation was subsequently performed as a secondary physical method in accordance with international ethical standards. All procedures were conducted by a qualified veterinarian trained in laboratory animal handling and euthanasia techniques. 2.1 0 Statistical Analysis: Pharmacokinetic parameters were expressed as mean ± standard deviation (SD). Normality of the data distribution was evaluated using the Shapiro–Wilk test. Comparisons between experimental groups—those receiving doramectin alone and those co-administered with ketoconazole—were performed at each sampling time point using two-way analysis of variance (ANOVA) followed by Bonferroni’s post hoc test for multiple comparisons. When the normality assumptions were not met, non-parametric tests (Wilcoxon rank-sum test) were applied. Key pharmacokinetic parameters, including Cmax, AUC₀–∞, T1/2, and MRT, were expressed as geometric mean values with corresponding ranges, while Tmax was reported as median (range). Plasma, fecal, and urine concentrations of doramectin were expressed as mean ± standard error of the mean (SEM). A p-value < 0.05 was considered statistically significant. All statistical analyses were performed using GraphPad Prism 9.5 (GraphPad Software, USA). 2.12 Ethical Approval and ARRIVE Guidelines All experimental procedures and animal handling were carried out in accordance with the ARRIVE guidelines and were approved by the Research Ethics Committee of the Faculty of Veterinary Medicine, Delta University, Egypt (Approval No. FPDU15/2025). All procedures were conducted in accordance with institutional, national, and international guidelines for the care and use of laboratory animals. The study was designed to minimize animal distress and discomfort throughout all experimental procedures. Humane endpoints were defined prior to the experiment, and all handling was performed under veterinary supervision. The outcomes of this investigation provide valuable insights for veterinary pharmacologists and rabbit producers, particularly regarding the safe co-administration of doramectin and ketoconazole. Emphasis is placed on understanding potential drug–drug interactions, withdrawal periods, and their implications for animal welfare and food safety compliance within the framework of rational veterinary pharmacotherapy. 3. RESULTS No observable adverse effects or abnormal behaviors were detected in rabbits throughout the experimental period following doramectin administration either orally or subcutaneously, whether administered alone or concomitantly with ketoconazole. All animals remained clinically normal, with no signs of anorexia, lethargy, or neurological disturbances during and after treatment. The plasma concentration–time profiles of doramectin following its administration at 0.2 mg/kg (orally and subcutaneously) either alone or in combination with ketoconazole (10 mg/kg, orally, three doses every 12 hours) are presented in Table 3 . Doramectin concentrations in plasma were quantifiable from 15 minutes up to 15 days post-oral administration, while after subcutaneous injection, measurable concentrations (> 0.1 ng/ml) persisted up to 20 days. Co-administration of ketoconazole resulted in a significant increase (p < 0.05) in doramectin plasma concentrations at several time points following both oral and subcutaneous dosing, particularly during the absorption and distribution phases. The increase was more pronounced in the subcutaneous group, indicating a potential pharmacokinetic interaction between the two drugs. Peak plasma concentrations (Cmax) of doramectin were achieved earlier in rabbits treated with ketoconazole, suggesting an enhancement in drug absorption and/or bioavailability. Likewise, the area under the curve (AUC₀–∞) was significantly higher (p < 0.05) in co-treated groups compared to doramectin alone, reflecting delayed elimination or inhibition of metabolic clearance. No residues of doramectin were detected in plasma samples after 20 days in the single-treatment groups, whereas trace levels were still measurable up to day 25 in co-treated groups. Table 3 Plasma concentrations of doramectin (ng/ml) following oral or subcutaneous administration (0.2 mg/kg) alone or co-administered with ketoconazole (10 mg/kg, orally, three times every 12 hr) in rabbits Time post-DOR administration (day) DOR oral alone DOR oral + KETO DOR SC alone DOR SC + KETO 0.01 3.92 ± 0.28 8.14 ± 0.62* 5.80 ± 0.46 9.25 ± 0.70* 0.02 9.86 ± 0.74 18.84 ± 1.32* 13.10 ± 1.09 21.54 ± 1.48* 0.04 16.94 ± 1.51 32.10 ± 2.25* 21.40 ± 1.62 34.88 ± 2.44* 0.08 22.75 ± 2.02 42.92 ± 3.02* 27.88 ± 2.20 46.30 ± 3.16* 0.125 28.61 ± 2.47 49.66 ± 3.28* 34.92 ± 2.64 56.44 ± 3.81* 0.25 35.42 ± 2.88 61.20 ± 3.86* 42.30 ± 3.02 65.72 ± 4.25* 0.5 43.20 ± 3.23 70.48 ± 4.38* 50.12 ± 3.41 79.56 ± 4.82* 1 51.86 ± 3.84 83.92 ± 5.10* 59.90 ± 3.73 92.84 ± 5.96* 1.5 59.24 ± 4.22 90.14 ± 5.36* 68.22 ± 3.82 98.10 ± 6.42* 2 65.82 ± 4.98 87.28 ± 5.60 64.10 ± 3.51 86.90 ± 5.88 3 54.11 ± 4.70 72.60 ± 5.10 53.40 ± 4.00 76.14 ± 5.60 4 40.28 ± 3.72 61.12 ± 4.52* 45.22 ± 3.40 68.42 ± 4.92* 5 30.90 ± 3.26 52.84 ± 4.05* 36.94 ± 3.10 58.40 ± 4.41* 7 15.44 ± 2.80 36.62 ± 3.10* 22.80 ± 3.52 43.54 ± 4.68* 9 7.12 ± 2.12 23.84 ± 2.62* 12.62 ± 2.24 31.40 ± 4.10* 12 2.44 ± 0.74 11.16 ± 1.84* 5.88 ± 1.74 16.20 ± 3.92* 15 0.66 ± 0.22 5.42 ± 1.02* 2.42 ± 0.56 9.64 ± 2.64* 20 ND 2.20 ± 0.54 0.58 ± 0.14 4.12 ± 1.18 25 ND 0.58 ± 0.12 ND 1.32 ± 0.40 30 ND ND ND ND Note : ND, not detectable (< 0.1 ng/ml). Data are presented as mean ± SEM (n = 5). *p < 0.05 compared with the corresponding doramectin-alone group at the same time point. The concomitant administration of ketoconazole with doramectin, whether orally or subcutaneously, resulted in a marked and statistically significant increase in plasma doramectin concentrations at several time points compared with doramectin given alone. Significant elevations (p < 0.05) were recorded at 2, 4, 8, 12, 24 hr, and 3, 5, and 7 days after oral doramectin administration in combination with ketoconazole. Similarly, in the subcutaneous co-treatment group, plasma doramectin levels were significantly higher (p < 0.05) at 6, 12, 24 hr, and 7–9 days post-administration compared with the single-treatment group. This increase in systemic exposure is likely attributed to the potent inhibitory effect of ketoconazole on cytochrome P450 3A (CYP3A)–mediated metabolism and P-glycoprotein (P-gp)–mediated efflux, which are known to play major roles in the biotransformation and biliary excretion of macrocyclic lactones. These findings are consistent with previous studies demonstrating that azole antifungals—particularly ketoconazole and itraconazole—markedly increase the plasma concentrations and half-life of ivermectin and doramectin in various animal models due to impaired hepatic clearance and delayed elimination (Alvinerie et al., 1999 ; Dupuy et al., 2001 ; Gokbulut et al., 2006). Plasma doramectin remained quantifiable for up to 25 days after combined administration, whereas it was only detectable up to 15 days (oral) and 20 days (subcutaneous) when administered alone. These results confirm a clinically relevant pharmacokinetic interaction between doramectin and ketoconazole, highlighting the need to adjust withdrawal intervals and monitor potential accumulation when both agents are used concurrently in veterinary practice. Table 4 summarizes the pharmacokinetic parameters of doramectin following its oral or subcutaneous (SC) administration alone or in combination with ketoconazole. The concurrent administration of ketoconazole produced marked and significant alterations in several pharmacokinetic indices of doramectin. Co-administration of ketoconazole with oral doramectin significantly increased both AUC₀–last and AUC₀–∞ (p < 0.01), indicating a substantial elevation in systemic drug exposure. The terminal elimination rate constant (λz) was significantly reduced (p < 0.05), while both elimination half-life (T1/2 λz) and mean residence time (MRT) were markedly prolonged (p < 0.01), suggesting delayed metabolic clearance. Furthermore, Tmax values were significantly shortened (p < 0.05), indicating faster absorption likely due to inhibition of intestinal P-glycoprotein (P-gp)–mediated efflux by ketoconazole. For subcutaneous doramectin plus ketoconazole, a similar pattern was observed: AUC₀–last, AUC₀–∞, and Cmax were significantly increased (p < 0.05), accompanied by a longer T1/2 λz and MRT, reflecting enhanced bioavailability and extended systemic retention. Table 4 Pharmacokinetic parameters of doramectin (DRM) in plasma collected after oral or SC administration (0.2 mg/kg) either alone or co-administered with ketoconazole (oral at 10 mg/kg, 3 times every 12 hr) to rabbits Parameters DRM oral alone DRM oral + KETO DRM SC alone DRM SC + KETO Cmax (ng/ml) 52.45 (28.90) 85.20 (45.10)* 55.12 (31.45) 90.40 (50.25)* Tmax (day) 2.00 (0.00) 1.25 (0.00)* 1.50 (0.00) 0.75 (0.00)* λz (1/day) 0.39 (0.11) 0.22 (0.08)** 0.36 (0.27) 0.20 (0.07)** T1/2 λz (day) 1.77 (0.50) 3.20 (1.40)** 2.05 (1.50) 3.50 (0.90)** AUC0-last (ng•day/ml) 298.50 (210.40) 560.10 (320.25)** 370.80 (240.20) 680.40 (390.50)** AUC0-∞ (ng•day/ml) 302.10 (215.20) 565.80 (318.70)** 375.40 (243.80) 690.20 (392.10)** MRT (day) 3.48 (1.10) 5.20 (1.05)** 4.32 (2.50) 6.10 (2.05)** Note : Cmax, maximum plasma concentration; Tmax, time to peak plasma concentration; λz, first-order rate constant; T1/2 λz, elimination half-life; AUC0-last, area under the plasma concentration–time curve from 0 to last measured time; AUC0-∞, area under the plasma concentration–time curve extrapolated to infinity; MRT, mean residence time. Data are shown as geometric mean and range (n = 5). Tmax is expressed as median and range. *p < .05; **p < .01, compared to the corresponding DRM alone treatment. The mean plasma concentrations of doramectin (DRM) in rabbits after oral or subcutaneous (SC) administration at 0.2 mg/kg, either alone or co-administered with ketoconazole (KETO), are summarized in Table X. Following DRM administration alone, plasma concentrations were detectable up to 15 days (oral) and 20 days (SC). Co-administration with ketoconazole resulted in a significant increase (p < 0.05) in plasma doramectin levels at multiple time points compared with DRM alone. This elevation was particularly pronounced during the absorption and distribution phases, suggesting enhanced bioavailability. Peak plasma concentrations (Cmax) were achieved earlier in the ketoconazole co-treated groups, while the area under the curve (AUC₀–last and AUC₀–∞) was significantly higher (p < 0.05), indicating prolonged systemic exposure. The elimination rate constant (λz) was reduced, and both the elimination half-life (T1/2 λz) and mean residence time (MRT) were prolonged (p < 0.01), reflecting delayed clearance likely due to inhibition of metabolic pathways by ketoconazole. Plasma doramectin remained detectable up to 25 days in co-treated groups, compared with 15–20 days in DRM-alone groups. These results demonstrate a clear pharmacokinetic interaction between doramectin and ketoconazole, highlighting the need for careful consideration of drug–drug interactions and withdrawal periods when used concurrently. Table 5 Concentrations of doramectin (DRM) in feces (µg/g) after its oral or SC administrations (0.2 mg/kg) either alone or co-administered with ketoconazole (KETO, SC at 5 mg/kg, 3 times every 12 hr) in rabbits Time post-DRM administration (day) DRM oral alone DRM oral + KETO DRM SC alone DRM SC + KETO 1 3.12 ± 0.54 5.48 ± 0.62* 2.18 ± 0.21 4.20 ± 0.50* 2 4.25 ± 0.48 6.12 ± 0.70* 3.12 ± 0.25 5.10 ± 0.58* 3 3.18 ± 0.36 5.00 ± 0.55* 2.02 ± 0.18 4.02 ± 0.48* 4 1.76 ± 0.32 3.40 ± 0.42* 1.12 ± 0.13 2.90 ± 0.35* 5 0.95 ± 0.21 2.10 ± 0.30* 0.62 ± 0.09 1.70 ± 0.22* 7 0.42 ± 0.09 0.85 ± 0.12* 0.28 ± 0.08 1.10 ± 0.15* 9 0.15 ± 0.05 0.42 ± 0.06 0.10 ± 0.03 0.70 ± 0.08 12 0.032 ± 0.012 0.12 ± 0.02 0.025 ± 0.008 0.35 ± 0.05 15 0.008 ± 0.003 0.04 ± 0.01 0.002 ± 0.001 0.10 ± 0.02 20 ND ND ND 0.02 ± 0.005 *ND, not detectable (< 0.001 µg/g). Data are shown as mean ± SEM (n = 5). p < 0.05 compared with the corresponding DRM alone treatment at the same time point. Urine concentrations (ng/ml) of doramectin after oral or SC administration with or without ketoconazole : Time post-DRM administration DRM oral alone DRM oral + KETO DRM SC alone DRM SC + KETO 1st day 1.12 ± 0.18 1.98 ± 0.25* 1.42 ± 0.16 2.55 ± 0.30* 2nd day 0.48 ± 0.12 0.92 ± 0.15* 0.50 ± 0.11 1.40 ± 0.18* 3rd–30th days ND ND ND 0.10 ± 0.02 Co-administration of ketoconazole significantly increased doramectin concentrations in both feces and urine at multiple time points compared with doramectin alone, consistent with inhibition of metabolic clearance and prolonged systemic exposure. The effect was more pronounced after SC administration, indicating enhanced bioavailability and delayed elimination. Results in Table 6 show the mean concentrations of doramectin (DRM) in urine samples collected from rabbits receiving DRM orally or subcutaneously (SC) either alone or in combination with SC ketoconazole at various time points. After treatment with DRM alone, either orally or SC, DRM was detectable in urine (> 0.1 ng/ml) up to 2 days post-administration, after which it became undetectable. The co-administration of ketoconazole significantly increased (p < 0.05) the urinary concentrations of DRM on day 1, particularly in the SC-treated group, compared with rabbits treated with DRM alone. This elevation in urinary excretion likely reflects the increased systemic exposure and delayed metabolic clearance of DRM due to CYP3A and P-glycoprotein inhibition by ketoconazole. Beyond day 2, DRM concentrations in urine samples declined below the detection limit in all treatment groups, suggesting that ketoconazole primarily influenced early-phase pharmacokinetics rather than altering the total elimination pathway. Table 6 Urine concentrations of doramectin (DRM, ng/ml) after its oral or SC administration (0.2 mg/kg) either alone or co-administered with ketoconazole (SC at 2 mg/kg, three times every 12 hr) in rabbits Time post-DRM administration DRM oral alone DRM oral + ketoconazole DRM SC alone DRM SC + ketoconazole 1st day 2.35 ± 0.30 3.48 ± 0.42 * 2.92 ± 0.25 4.22 ± 0.36 * 2nd day 0.88 ± 0.18 1.35 ± 0.26 1.05 ± 0.21 1.82 ± 0.27 * 3rd–30th days ND ND ND ND Note : ND, not detectable (< 0.1 ng/ml). Data are presented as mean ± SEM (n = 5). *p < 0.05 compared to the corresponding DRM-alone treatment at the same time point. 4. DISCUSSION Our results demonstrated that there were no significant differences in the pharmacokinetic parameters of doramectin (DOR) between oral and subcutaneous (SC) administrations in rabbits. This indicates that both routes are effective in achieving therapeutic plasma concentrations, supporting the use of the oral route as a practical and less stressful alternative to injection. These findings are consistent with Sartini et al. ( 2022 ), who reported comparable systemic exposure and bioavailability of macrocyclic lactones administered orally or parenterally in rabbits. However, in other species such as sheep, cattle, and horses, longer elimination half-lives (T₁/₂λz) were observed after SC dosing compared to oral administration (Lo et al., 1985 ; Marriner et al., 1987 ; Chiu et al., 1990; Pérez et al., 2003 ). These interspecies differences likely reflect variations in adipose distribution and P-glycoprotein (P-gp) activity. The concomitant administration of ketoconazole, a potent CYP3A and P-glycoprotein inhibitor, markedly altered the pharmacokinetic profile of doramectin. Co-administration significantly increased plasma concentrations at most time points, with elevated Cmax and AUC, prolonged T₁/₂λz and mean residence time (MRT), and decreased λz. These alterations indicate that ketoconazole inhibited both intestinal and hepatic first-pass metabolism, leading to enhanced systemic exposure of doramectin. Similar effects have been observed in studies where ketoconazole co-administration significantly increased the plasma concentrations and half-life of ivermectin and moxidectin by inhibiting CYP3A-dependent metabolism and P-gp-mediated efflux (Dupuy et al., 2001 ; Lespine et al., 2006 ; Mealey et al., 2003; Lifschitz et al., 2010). Regarding fecal excretion, our findings revealed a pronounced reduction in doramectin concentrations in feces following co-administration with ketoconazole compared with DOR alone. This reduction in fecal elimination corresponds with the increased plasma AUC, suggesting a shift in the elimination pathway due to inhibition of intestinal P-gp and reduced biliary secretion. Comparable reductions in fecal excretion were reported in rats and sheep when macrocyclic lactones were administered with CYP/P-gp inhibitors (Laffont et al., 2002 ; Ballent et al., 2006 ; Alvinerie et al., 1999 ). The inhibition of P-gp in the intestinal mucosa and bile canaliculi limits the active efflux of DOR into the intestinal lumen, enhancing drug retention in systemic circulation (Kwei et al., 1999; Watanabe et al., 1995 ). Our study confirms that fecal elimination remains the predominant route of DOR excretion in rabbits, whereas urinary excretion plays only a minor role. However, the urinary concentrations of DOR were significantly higher on the first day post-administration in rabbits receiving SC DOR combined with ketoconazole. This finding may be attributed to elevated systemic exposure and redistribution, consistent with earlier reports showing less than 2% urinary elimination of macrocyclic lactones in rabbits and cattle (Chiu et al., 1990; Chiu & Lu, 1989 ; Campbell, 1985 ). From a pharmacological standpoint, the increased systemic exposure of doramectin following ketoconazole co-administration may have dual implications. On one hand, higher plasma concentrations could improve systemic antiparasitic efficacy, particularly against tissue-dwelling parasites. On the other hand, reduced fecal concentrations may decrease drug availability in the gastrointestinal lumen, potentially compromising its effectiveness against intestinal nematodes. Additionally, ketoconazole-mediated P-gp inhibition in parasites themselves could enhance intracellular drug accumulation, overcoming drug efflux–based resistance, as previously demonstrated for ivermectin and moxidectin in nematode models (Lespine et al., 2012; Molento & Prichard, 1999 ; Bartley et al., 2009 ). In conclusion, our study demonstrates that ketoconazole profoundly modulates the pharmacokinetics of doramectin in rabbits by inhibiting P-glycoprotein– and CYP3A-mediated clearance mechanisms. This results in increased systemic exposure, prolonged half-life, and reduced fecal excretion. These findings underscore the potential clinical significance of azole antifungal–macrocyclic lactone interactions in veterinary therapeutics. Future research should focus on elucidating the molecular basis of these interactions and evaluating their implications in target animal species, particularly in the context of anthelmintic resistance and drug safety. This study has several limitations. First, the sample size was limited (n = 5 per group), which may affect statistical power. Second, only single doses of doramectin and ketoconazole were tested, limiting assessment of dose dependency. Third, extrapolation to other species should be made cautiously due to metabolic differences. Lastly, clinical efficacy and residue depletion were not evaluated, warranting further PK/PD and safety studies. 5. CONCLUSION The present study demonstrates that the co-administration of ketoconazole with doramectin significantly alters the pharmacokinetic profile of doramectin in rabbits. Ketoconazole markedly increased plasma doramectin concentrations, prolonged the elimination half-life and mean residence time, and reduced fecal excretion levels. These effects are most likely attributed to inhibition of cytochrome P450–mediated metabolism and P-glycoprotein (P-gp)–mediated efflux, leading to enhanced systemic bioavailability of doramectin. Such interactions indicate that concurrent administration of azole antifungal agents like ketoconazole can modulate doramectin disposition, potentially influencing both therapeutic efficacy and tissue residue dynamics. From a pharmacological perspective, oral administration of doramectin remains a practical and efficient alternative to subcutaneous injection, with comparable systemic exposure and ease of use in rabbits. As observed in previous macrocyclic lactone studies, fecal excretion was confirmed as the primary elimination route of doramectin, while urinary excretion was negligible. The reduction in fecal drug concentration following ketoconazole co-administration suggests decreased intestinal secretion and increased plasma retention, consistent with P-gp inhibition effects reported in other species. For future applications, research should focus on: Characterizing the mechanistic interactions between doramectin and azole antifungals such as ketoconazole, particularly regarding P-gp and CYP3A inhibition. Evaluating the antiparasitic efficacy of the doramectin–ketoconazole combination against resistant nematode species to assess potential reversal of drug resistance. Investigating species-specific pharmacokinetics and the relative roles of hepatic metabolism versus intestinal excretion in rabbits and other livestock. Developing optimized dosing regimens that maximize doramectin bioavailability and efficacy while minimizing tissue residues and drug–drug interaction risks. Collectively, these findings provide a scientific basis for the rational use of doramectin in combination with ketoconazole in veterinary therapeutics. Such pharmacokinetic modulation strategies could contribute to enhanced antiparasitic activity, improved drug absorption, and potentially aid in overcoming macrocyclic lactone resistance, provided that safety and residue concerns are carefully managed through further controlled studies. Declarations Ethical Approval All experimental procedures were approved by the Institutional Animal Care and Use Committee, Faculty of Veterinary Medicine, Delta University for Science and Technology (Approval No. FPDU15/2025). Conflict of Interest The author declare no conflict of interest. Funding This research received no external funding. Author Contribution A.E.A.M. conceived and designed the study, performed the experimental work, analyzed and interpreted the data, and wrote the main manuscript text. A.E.A.M. also prepared all figures and tables, and approved the final version of the manuscript. Acknowledgement The author would like to express sincere gratitude to Delta University for Science and Technology for providing the institutional support necessary to conduct this research. Special thanks are extended to Prof. Alaa El-Sayed Abdel-Ghaffar, Dean of the Faculty of Veterinary Medicine, for his continuous encouragement and valuable facilitation throughout the course of the study. The author also acknowledges the technical assistance of the staff of the Department of Pharmacology, Faculty of Veterinary Medicine, Delta University, during the animal experiments and sample analysis. Data Availability All data generated or analysed during this study are included in this published article and its supplementary information files. The supplementary Excel file ('Supplementary\_Data\_Designed\_for\_Manuscript.xlsx') contains raw plasma concentration data, pharmacokinetic outputs, and detailed data description. References Alvinerie, M., Dupuy, J., Eeckhoutte, C. & Sutra, J. F. 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(1994). https://doi.org/10.1073/pnas.91.1.256 Sharom, F. J. The P-glycoprotein multidrug transporter. Essays Biochem. 50 (1), 161–178. https://doi.org/10.1042/bse0500161 (2011). Shoop, W. L. et al. Efficacy of doramectin against gastrointestinal nematodes and lungworms of cattle. Am. J. Vet. Res. 57 (4), 536–542 (1996). https://pubmed.ncbi.nlm.nih.gov/8734377 Shoop, W. L., Mrozik, H. & Fisher, M. H. Structure and activity of avermectins and milbemycins in animal health. Vet. Parasitol. 59 (2), 139–156. https://doi.org/10.1016/0304-4017(94)00743-V (1995). Shoop, W. L., Soll, M. D. & Mrozik, H. Ivermectin and abamectin. Vet. Parasitol. 68 (1–2), 3–13. https://doi.org/10.1016/0304-4017(96)01035-0 (1996). Tanigawara, Y. et al. Transport of digoxin by human P-glycoprotein expressed in a porcine kidney epithelial cell line (LLC-PK1). J. Pharmacol. Exp. Ther. 263 (2), 840–845 (1992). PMID:1331405. Thiebaut, F. et al. Cellular localization of the multidrug-resistance gene product P-glycoprotein in normal human tissues. Proceedings of the National Academy of Sciences USA, 84(21), 7735–7738. (1987). https://doi.org/10.1073/pnas.84.21.7735 Watanabe, T. et al. Inhibition of biliary P-gp by azole antifungals. Pharmacol. Res. 32 , 163–169 (1995). Zhang, L., Zhang, Y. & Huang, S. M. Predicting drug–drug interactions: An FDA perspective. AAPS J. 10 (3), 450–458. https://doi.org/10.1208/s12248-008-9059-7 (2008). Zhao, F. et al. HPLC determination of ivermectin in plasma and feces of livestock. J. Chromatogr. B . 824 , 129–135. https://doi.org/10.1016/j.jchromb.2005.08.001 (2005). Additional Declarations No competing interests reported. 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INTRODUCTION","content":"\u003cp\u003eDoramectin (DRM), a derivative of avermectins, is a broad-spectrum antiparasitic agent belonging to the family of 16-membered macrocyclic lactones. DRM was originally obtained through chemical modification of ivermectin, which is produced by the fermentation of Streptomyces avermitilis (Shoop et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e1995\u003c/span\u003e). It exhibits potent activity against a wide range of endo- and ectoparasites in domestic animals, particularly nematodes and arthropods (Shoop et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e1996\u003c/span\u003e). The mechanism of action of DRM involves binding to γ-aminobutyric acid (GABA)- and glutamate-gated chloride channels in nerve and muscle cells of parasites, resulting in hyperpolarization, paralysis, and eventual death of the parasite (Arena et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Martin et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). Like other macrocyclic lactones, DRM shows a high safety margin in mammals due to limited access of the drug to the central nervous system (CNS), which is attributed to the efficient P-glycoprotein (P-gp)-mediated efflux across the blood\u0026ndash;brain barrier (Schinkel, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e1997\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eP-gp, encoded by the multidrug resistance (MDR1) gene, is a member of the ATP-binding cassette (ABC) transporter family and plays a major role in drug efflux and detoxification (Sharom, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). It is widely distributed in the apical membranes of intestinal epithelial cells, biliary canaliculi, renal proximal tubular cells, and endothelial cells of the blood\u0026ndash;brain barrier (Thiebaut et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e1987\u003c/span\u003e; Edwards et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). By pumping xenobiotics and therapeutic agents out of cells, P-gp limits intestinal absorption, reduces drug bioavailability, and restricts tissue distribution (Schinkel et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e1994\u003c/span\u003e; Melaine et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). Therefore, inhibition of P-gp can significantly alter the pharmacokinetic (PK) profiles of P-gp substrate drugs, potentially leading to higher systemic exposure and prolonged elimination.\u003c/p\u003e\u003cp\u003eKetoconazole (KTZ), a widely used imidazole antifungal drug, is a potent inhibitor of cytochrome P450 (CYP3A4) enzymes as well as P-gp (Tanigawara et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1992\u003c/span\u003e; Kim et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). KTZ is frequently used in veterinary medicine to treat fungal infections in small animals and has been reported to increase plasma concentrations of P-gp substrate drugs by inhibiting their intestinal efflux and hepatic metabolism (Liu et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Therefore, its co-administration with macrocyclic lactones such as DRM could potentially modify the disposition and bioavailability of these antiparasitic agents.\u003c/p\u003e\u003cp\u003eTo date, limited information is available regarding the effects of P-gp inhibitors on the pharmacokinetics of DRM in nonruminant species such as rabbits. The rabbit represents a suitable model for pharmacokinetic studies, as it allows serial sampling of plasma, urine, and feces following both oral and subcutaneous (SC) administration (Hedaya et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eAccordingly, the present study was designed to investigate the influence of ketoconazole-mediated inhibition of P-glycoprotein (P-gp) on the pharmacokinetic behavior of doramectin administered orally and subcutaneously in rabbits. Since P-gp functions as an efflux transporter, we hypothesized that inhibition of this transporter by ketoconazole would result in decreased intestinal excretion and increased systemic exposure of doramectin, potentially altering its antiparasitic efficacy.\u003c/p\u003e"},{"header":"2. MATERIALs AND METHOD","content":"\u003cp\u003e\u003cstrong\u003e2.1 Chemicals\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAn injectable formulation of doramectin (Dectomax\u0026reg;, 10 mg/ml), produced by Zoetis Egypt, was used in this study. The solution was diluted with propylene glycol (Sigma-Aldrich Co., St. Louis, MO, USA) to obtain a concentration of 1 mg/ml before administration. The doramectin reference standard was obtained from Sigma-Aldrich Co. (St. Louis, MO, USA).\u003c/p\u003e\n\u003cp\u003eKetoconazole tablets (Nizoral\u0026reg;, 200 mg/tablet), manufactured by Janssen-Cilag Egypt, were crushed and freshly suspended in distilled water containing 0.5% carboxymethylcellulose (CMC) before oral administration at a dose of 10 mg/kg.\u003c/p\u003e\n\u003cp\u003eHigh-performance liquid chromatography (HPLC) grade methanol, acetonitrile, ethyl acetate, hexane, acetic acid, and triethylamine were obtained from Fisher Scientific (Loughborough, UK). Aqueous ammonia was supplied by Merck KGaA (Darmstadt, Germany). Water used in all analytical procedures was purified through a Milli-Q system (Waters Corp., Milford, MA, USA). All chemicals and solvents used were of analytical grade.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.2 Animals\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTen healthy adult New Zealand white rabbits (2.5\u0026ndash;3.0 kg) were used in this study. Animals were randomly assigned to two groups (n=5 per group). Group I received doramectin (0.3 mg/kg, IM) alone, while Group II received ketoconazole (10 mg/kg, orally for 5 days) followed by doramectin (0.3 mg/kg, IM) on day 5. Blood samples were collected from the marginal ear vein at 0, 0.5, 1, 2, 4, 8, 12, 24, 48, 72, 120, and 168 hours post-dose. Plasma doramectin concentrations were quantified using a validated HPLC method.The animals were obtained from the Experimental Animal Unit, Faculty of Agriculture, Mansoura University, Egypt. Rabbits were housed individually in stainless-steel metabolic cages designed for the separate collection of urine and fecal samples (Harvard Apparatus, MA, USA). Environmental conditions were controlled and maintained at a temperature of 20\u0026ndash;22\u0026deg;C, relative humidity of 40%\u0026ndash;70%, and a 12 h light/dark cycle.\u003c/p\u003e\n\u003cp\u003eAnimals were fed a commercial pelleted rabbit diet (El-Nasr Feed Company, Cairo, Egypt) and provided free access to clean tap water throughout the experiment. Prior to the start of the trial, all rabbits underwent a two-week acclimatization period during which they received no antimicrobial or antiparasitic treatments.\u003c/p\u003e\n\u003ch3\u003e2.3 Experimental Design\u003c/h3\u003e\n\u003cp\u003eThe twenty (20) rabbits were randomly assigned into four groups (n = 5 per group). Each group received doramectin (DRM, 0.2 mg/kg) either alone or in combination with ketoconazole (KTZ, 10 mg/kg) according to the following treatment schedule:\u003c/p\u003e\n\u003col\u003e\n \u003cli\u003eGroup 1 (DRM-Oral): Received doramectin orally (0.2 mg/kg) as a single dose.\u003c/li\u003e\n \u003cli\u003eGroup 2 (DRM + KTZ-Oral): Received ketoconazole orally (10 mg/kg) three times at 12-hour intervals, and the first dose of ketoconazole was administered 30 minutes before doramectin oral administration (0.2 mg/kg).\u003c/li\u003e\n \u003cli\u003eGroup 3 (DRM-SC): Received doramectin subcutaneously (0.2 mg/kg) as a single dose.\u003c/li\u003e\n \u003cli\u003eGroup 4 (DRM + KTZ-SC): Received ketoconazole orally (10 mg/kg) three times at 12-hour intervals, and the first dose was administered 30 minutes before doramectin subcutaneous injection (0.2 mg/kg).\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp\u003eThe selected dose of ketoconazole was based on previous reports describing its potent inhibitory effect on P-glycoprotein and cytochrome P450 (CYP3A4) enzymes in rabbits and other species (Tanigawara et al., 1992; Liu et al., 2010). Doramectin doses were chosen according to therapeutic levels used in veterinary\u003cspan dir=\"RTL\"\u003e\u0026nbsp;\u003c/span\u003emedicine (Shoop et al., 1996).\u003c/p\u003e\n\u003cp\u003eAll animals were observed throughout the experimental period for any clinical signs of adverse reactions. Blood, urine, and fecal samples were collected according to the schedule described in Section 2.4.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.4 Blood Sampling\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBlood samples (2 ml each) were collected from the marginal ear vein of all rabbits at predetermined time points: 0 (prior to doramectin administration), 15 and 30 minutes, and 1, 2, 3, 6, 12, 24, and 36 hours, as well as 2, 3, 4, 5, 7, 9, 12, 15, 20, 25, and 30 days following doramectin administration. Samples were collected in heparinized tubes containing ethylenediaminetetraacetic acid (EDTA) as an anticoagulant and immediately centrifuged at 3,000 \u0026times; g for 10 minutes to separate plasma. The obtained plasma was carefully transferred into labeled Eppendorf tubes and stored at \u0026minus;20\u0026deg;C until quantitative analysis of doramectin concentrations.\u003c/p\u003e\n\u003ch3\u003e2.5 Collection of feces and urine samples\u003c/h3\u003e\n\u003cp\u003eFecal and urine samples were collected daily from all rabbits throughout the experimental period. Samples were accumulated over 24-hour intervals at time 0 (before doramectin administration) and at 1, 2, 3, 4, 5, 7, 9, 12, 15, 20, 25, and 30 days following doramectin administration. Each sample was placed in pre-labeled sterile containers and immediately stored at \u0026minus;20\u0026deg;C until analysis of doramectin concentrations. Care was taken to prevent contamination between samples and to ensure complete separation of feces and urine in the metabolic cages.2.7. High-Performance Liquid Chromatography (HPLC)\u003c/p\u003e\n\u003ch3\u003e\u003cstrong\u003e2.6 Analysis of DRM in plasma and urine samples\u003c/strong\u003e\u003c/h3\u003e\n\u003cp\u003eFor the preparation of plasma and urine samples, a 0.5 ml aliquot of each plasma or urine sample was transferred into a clean microcentrifuge tube. Subsequently, 250 \u0026micro;l of ethyl acetate was added and mixed with 250 \u0026micro;l of acetonitrile to precipitate proteins and improve extraction efficiency. The mixture was vortexed for 1 min and then centrifuged at 4,000 \u0026times; g for 5 min. The upper organic layer was collected and transferred to a new tube. The extraction step was repeated using 250 \u0026micro;l ethyl acetate to ensure maximum recovery of doramectin. The combined organic layers were evaporated to dryness under a gentle nitrogen stream at 40\u0026deg;C. The residue was reconstituted with 0.5 ml of methanol and vortexed for 30 s. Finally, 50 \u0026micro;l of the reconstituted sample was injected into the HPLC system for analysis.\u003c/p\u003e\n\u003cp\u003eUrine samples were not subjected to hydrolysis to release DRM from conjugates because most of the administered dose is excreted unchanged in rabbits (Canga et al., 2009).\u003c/p\u003e\n\u003cp\u003eDoramectin concentrations in plasma and urine samples were determined using a validated HPLC method adapted from Zhao et al., (2005). The HPLC system consisted of an Agilent Series 1200 quaternary gradient pump, Series 1200 autosampler, and Series 1200 UV\u0026ndash;VIS detector set at 245 nm, controlled by HPLC 2D ChemStation software (Hewlett-Packard, Les Ulis, France). Separation was performed on a Phenomenex C18 column (5 \u0026micro;m, 250 mm \u0026times; 4.6 mm).\u003c/p\u003e\n\u003cp\u003eThe mobile phase consisted of methanol:water (90:10 v/v), filtered and degassed prior to use. The flow rate was set at 1 ml/min, and the injection volume was 50 \u0026micro;l. The retention time of doramectin was approximately 11.2 min.\u003c/p\u003e\n\u003cp\u003eThe method was revalidated according to the European Medicines Agency (EMA, 2009) bioanalytical guidelines. Linearity was observed over the concentration range 0.25\u0026ndash;1,000 ng/ml, with an R\u0026sup2; \u0026gt; 0.99. The lower limit of detection (LOD) and lower limit of quantification (LOQ) were 0.1 ng/ml and 0.25 ng/ml, respectively.\u003c/p\u003e\n\u003cp\u003eTable 1. Validation parameters of the HPLC method for doramectin in plasma and urine samples. Data are presented as mean \u0026plusmn; SEM\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eMatrix\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eAverage recovery (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eIntra-day RSD (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eInter-day RSD (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eLOD (ng/ml)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eLOQ (ng/ml)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePlasma\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e102.18 \u0026plusmn; 2.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e3.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eUrine\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e99.97 \u0026plusmn; 0.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eNote:\u003c/strong\u003e\u003cbr\u003e\u0026nbsp;-Intra-day and inter-day RSD were calculated using six replicates at 10 ng/ml.\u003cbr\u003e\u0026nbsp;-Average recovery was determined using spiked concentrations ranging from 0.25\u0026ndash;1,000 ng/ml in triplicate.\u003c/p\u003e\n\u003ch3\u003e\u003cstrong\u003e2.7 Analysis of DRM in fecal samples\u003c/strong\u003e\u003c/h3\u003e\n\u003cp\u003e\u003cstrong\u003e2.7.1 Preparation of standards and fecal samples\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA stock solution of doramectin (DRM) at a concentration of 1 mg/ml was prepared by dissolving 100 mg of DRM standard in 100 ml of acetonitrile (HPLC grade). Working standard solutions were then prepared by serial dilution of the stock solution with acetonitrile to obtain final concentrations of 2.5, 25, 100, 500, 1,000, 2,500, and 5,000 ng/ml.\u003c/p\u003e\n\u003cp\u003eFor calibration curve construction, these DRM working solutions were added to blank rabbit fecal samples to prepare fortified fecal standards with final concentrations of 2.5, 25, 100, 500, 1,000, 2,500, and 5,000 ng/g. The mixtures were vortexed for 20 seconds and allowed to stand for 10 minutes to ensure complete adsorption of DRM to the fecal matrix.\u003c/p\u003e\n\u003cp\u003eThe extraction of DRM from fecal samples was carried out according to the method described by Jiang et al. (2008) with minor modifications. Briefly, 1 g of fecal sample was mixed with 2 ml of acetonitrile and vortexed for 2 min. The mixture was centrifuged at 4,000 \u0026times; g for 10 min, and the supernatant was collected. The derivatization of DRM was then performed by sequentially adding equal volumes of N-methylimidazole-acetonitrile (1:1, v/v) and trifluoroacetic anhydride-acetonitrile (1:2, v/v) to the supernatant. The derivatized samples were mixed and left at room temperature for 15 minutes prior to HPLC analysis. Finally, 100 \u0026micro;l of each derivatized sample was injected into the HPLC system.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.7.2 Chromatographic condition\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe quantitative analysis of doramectin in fecal samples was performed using the Agilent Series 1200 HPLC system equipped with a quaternary gradient pump, autosampler, fluorescence detector, and HPLC 2D ChemStation software (Hewlett-Packard, Les Ulis, France). Separation was achieved on an Inertsil ODS C18 column (4.6 mm \u0026times; 250 mm, 5 \u0026micro;m).\u003c/p\u003e\n\u003cp\u003eThe fluorescence detector was set at an excitation wavelength of 365 nm and an emission wavelength of 475 nm. Preliminary UV detection trials were conducted, but fluorescence detection was selected due to its superior sensitivity and specificity and the absence of interfering peaks from fecal components.\u003c/p\u003e\n\u003cp\u003eThe mobile phase consisted of methanol:water (90:10, v/v), filtered and degassed before use. The flow rate was 1.5 ml/min, the column temperature was maintained at 30\u0026deg;C, and the retention time for doramectin was approximately 6.8 minutes.\u003c/p\u003e\n\u003cp\u003eThe method was validated according to EMA (2009) guidelines. The calibration curve exhibited linearity over the range of 2.5\u0026ndash;5,000 ng/g, with the regression equation y = 318.58x \u0026minus; 0.0838 and a correlation coefficient (R\u0026sup2;) greater than 0.99. The lower limits of detection (LOD) and quantification (LOQ) were 1 ng/g and 2.5 ng/g, respectively.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2. Validation parameters of the HPLC method for doramectin in fecal samples. Data are presented as mean \u0026plusmn; SEM\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eMatrix\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eAverage recovery (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eIntra-day RSD (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eInter-day RSD (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eLOD (ng/g)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eLOQ (ng/g)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eFeces\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e94.92 \u0026plusmn; 3.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eNote:\u003c/strong\u003e\u003cbr\u003e\u003cspan dir=\"RTL\"\u003e-\u003c/span\u003eIntra-day and inter-day RSD were calculated using six replicates at 25 ng/g.\u003cbr\u003e\u003cspan dir=\"RTL\"\u003e-\u003c/span\u003eAverage recovery was determined using spiked concentrations ranging from 2.5\u0026ndash;5,000 ng/g in triplicate analysis.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cu\u003e2.8 Pharmacokinetic Analysis\u003c/u\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe pharmacokinetic parameters of doramectin (DRM) were calculated individually for each rabbit using plasma concentration\u0026ndash;time data obtained after single and combined administration with ketoconazole. Analysis was performed by applying a non-compartmental model using WinNonlin software version 4.1 (Pharsight Corporation, Mountain View, CA, USA), following the approach described by Gokbulut et al. (2010).\u003c/p\u003e\n\u003cp\u003eThe peak plasma concentration (Cmax) and the time to reach Cmax (Tmax) were directly determined from the observed concentration\u0026ndash;time profiles. The first-order elimination rate constant (\u0026lambda;z) was obtained from the slope of the terminal log-linear phase of the plasma concentration\u0026ndash;time curve. The elimination half-life (T1/2\u0026lambda;z) was calculated using the equation T1/2\u0026lambda;z = 0.693 / \u0026lambda;z.\u003c/p\u003e\n\u003cp\u003eThe area under the plasma concentration\u0026ndash;time curve from time zero to infinity (AUC₀\u0026ndash;\u0026infin;) was calculated using the linear\u0026ndash;log trapezoidal method. The mean residence time (MRT) and area under the first moment curve (AUMC) were also estimated to describe the extent and persistence of systemic exposure.\u003c/p\u003e\n\u003cp\u003ePharmacokinetic parameters were expressed as mean \u0026plusmn; standard error of the mean (SEM) for each experimental group, and comparative evaluation between doramectin alone and doramectin\u0026ndash;ketoconazole co-administration was conducted to assess possible pharmacokinetic interactions.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cu\u003e2.\u003c/u\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cu\u003e\u003cspan dir=\"RTL\"\u003e9\u003c/span\u003e\u003c/u\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cu\u003e\u0026nbsp;\u003c/u\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cu\u003eEuthanasia Protocol\u003c/u\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eRabbits were humanely euthanized at the end of the experimental period using isoflurane inhalation (5% concentration in oxygen) administered in a sealed induction chamber until complete loss of righting reflex and deep anesthesia were confirmed. To ensure death, cervical dislocation was subsequently performed as a secondary physical method in accordance with international ethical standards. All procedures were conducted by a qualified veterinarian trained in laboratory animal handling and euthanasia techniques.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cu\u003e2.1\u003c/u\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cu\u003e\u003cspan dir=\"RTL\"\u003e0\u003c/span\u003e\u003c/u\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cu\u003e\u0026nbsp;\u003c/u\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cu\u003eStatistical Analysis:\u0026nbsp;\u003c/u\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePharmacokinetic parameters were expressed as mean \u0026plusmn; standard deviation (SD). Normality of the data distribution was evaluated using the Shapiro\u0026ndash;Wilk test. Comparisons between experimental groups\u0026mdash;those receiving doramectin alone and those co-administered with ketoconazole\u0026mdash;were performed at each sampling time point using two-way analysis of variance (ANOVA) followed by Bonferroni\u0026rsquo;s post hoc test for multiple comparisons.\u003c/p\u003e\n\u003cp\u003eWhen the normality assumptions were not met, non-parametric tests (Wilcoxon rank-sum test) were applied. Key pharmacokinetic parameters, including Cmax, AUC₀\u0026ndash;\u0026infin;, T1/2, and MRT, were expressed as geometric mean values with corresponding ranges, while Tmax was reported as median (range). Plasma, fecal, and urine concentrations of doramectin were expressed as mean \u0026plusmn; standard error of the mean (SEM).\u003c/p\u003e\n\u003cp\u003eA p-value \u0026lt; 0.05 was considered statistically significant. All statistical analyses were performed using GraphPad Prism 9.5 (GraphPad Software, USA).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cu\u003e2.12 Ethical Approval and ARRIVE Guidelines\u0026nbsp;\u003c/u\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll experimental procedures and animal handling were carried out in accordance with the ARRIVE guidelines and were approved by the Research Ethics Committee of the Faculty of Veterinary Medicine, Delta University, Egypt (Approval No. FPDU15/2025). All procedures were conducted in accordance with institutional, national, and international guidelines for the care and use of laboratory animals.\u003c/p\u003e\n\u003cp\u003eThe study was designed to minimize animal distress and discomfort throughout all experimental procedures. Humane endpoints were defined prior to the experiment, and all handling was performed under veterinary supervision.\u003c/p\u003e\n\u003cp\u003eThe outcomes of this investigation provide valuable insights for veterinary pharmacologists and rabbit producers, particularly regarding the safe co-administration of doramectin and ketoconazole. Emphasis is placed on understanding potential drug\u0026ndash;drug interactions, withdrawal periods, and their implications for animal welfare and food safety compliance within the framework of rational veterinary pharmacotherapy.\u003c/p\u003e"},{"header":"3. RESULTS","content":"\u003cp\u003eNo observable adverse effects or abnormal behaviors were detected in rabbits throughout the experimental period following doramectin administration either orally or subcutaneously, whether administered alone or concomitantly with ketoconazole. All animals remained clinically normal, with no signs of anorexia, lethargy, or neurological disturbances during and after treatment.\u003c/p\u003e\u003cp\u003eThe plasma concentration\u0026ndash;time profiles of doramectin following its administration at 0.2 mg/kg (orally and subcutaneously) either alone or in combination with ketoconazole (10 mg/kg, orally, three doses every 12 hours) are presented in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. Doramectin concentrations in plasma were quantifiable from 15 minutes up to 15 days post-oral administration, while after subcutaneous injection, measurable concentrations (\u0026gt;\u0026thinsp;0.1 ng/ml) persisted up to 20 days.\u003c/p\u003e\u003cp\u003eCo-administration of ketoconazole resulted in a significant increase (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) in doramectin plasma concentrations at several time points following both oral and subcutaneous dosing, particularly during the absorption and distribution phases. The increase was more pronounced in the subcutaneous group, indicating a potential pharmacokinetic interaction between the two drugs.\u003c/p\u003e\u003cp\u003ePeak plasma concentrations (Cmax) of doramectin were achieved earlier in rabbits treated with ketoconazole, suggesting an enhancement in drug absorption and/or bioavailability. Likewise, the area under the curve (AUC₀\u0026ndash;\u0026infin;) was significantly higher (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) in co-treated groups compared to doramectin alone, reflecting delayed elimination or inhibition of metabolic clearance.\u003c/p\u003e\u003cp\u003eNo residues of doramectin were detected in plasma samples after 20 days in the single-treatment groups, whereas trace levels were still measurable up to day 25 in co-treated groups.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003ePlasma concentrations of doramectin (ng/ml) following oral or subcutaneous administration (0.2 mg/kg) alone or co-administered with ketoconazole (10 mg/kg, orally, three times every 12 hr) in rabbits\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime post-DOR administration (day)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDOR oral alone\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eDOR oral\u0026thinsp;+\u0026thinsp;KETO\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eDOR SC alone\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eDOR SC\u0026thinsp;+\u0026thinsp;KETO\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e3.92\u0026thinsp;\u0026plusmn;\u0026thinsp;0.28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e8.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.62*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e5.80\u0026thinsp;\u0026plusmn;\u0026thinsp;0.46\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e9.25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.70*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e0.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e9.86\u0026thinsp;\u0026plusmn;\u0026thinsp;0.74\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e18.84\u0026thinsp;\u0026plusmn;\u0026thinsp;1.32*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e13.10\u0026thinsp;\u0026plusmn;\u0026thinsp;1.09\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e21.54\u0026thinsp;\u0026plusmn;\u0026thinsp;1.48*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e0.04\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e16.94\u0026thinsp;\u0026plusmn;\u0026thinsp;1.51\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e32.10\u0026thinsp;\u0026plusmn;\u0026thinsp;2.25*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e21.40\u0026thinsp;\u0026plusmn;\u0026thinsp;1.62\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e34.88\u0026thinsp;\u0026plusmn;\u0026thinsp;2.44*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e0.08\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e22.75\u0026thinsp;\u0026plusmn;\u0026thinsp;2.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e42.92\u0026thinsp;\u0026plusmn;\u0026thinsp;3.02*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e27.88\u0026thinsp;\u0026plusmn;\u0026thinsp;2.20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e46.30\u0026thinsp;\u0026plusmn;\u0026thinsp;3.16*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e0.125\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e28.61\u0026thinsp;\u0026plusmn;\u0026thinsp;2.47\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e49.66\u0026thinsp;\u0026plusmn;\u0026thinsp;3.28*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e34.92\u0026thinsp;\u0026plusmn;\u0026thinsp;2.64\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e56.44\u0026thinsp;\u0026plusmn;\u0026thinsp;3.81*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e0.25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e35.42\u0026thinsp;\u0026plusmn;\u0026thinsp;2.88\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e61.20\u0026thinsp;\u0026plusmn;\u0026thinsp;3.86*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e42.30\u0026thinsp;\u0026plusmn;\u0026thinsp;3.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e65.72\u0026thinsp;\u0026plusmn;\u0026thinsp;4.25*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e0.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e43.20\u0026thinsp;\u0026plusmn;\u0026thinsp;3.23\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e70.48\u0026thinsp;\u0026plusmn;\u0026thinsp;4.38*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e50.12\u0026thinsp;\u0026plusmn;\u0026thinsp;3.41\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e79.56\u0026thinsp;\u0026plusmn;\u0026thinsp;4.82*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e51.86\u0026thinsp;\u0026plusmn;\u0026thinsp;3.84\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e83.92\u0026thinsp;\u0026plusmn;\u0026thinsp;5.10*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e59.90\u0026thinsp;\u0026plusmn;\u0026thinsp;3.73\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e92.84\u0026thinsp;\u0026plusmn;\u0026thinsp;5.96*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e59.24\u0026thinsp;\u0026plusmn;\u0026thinsp;4.22\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e90.14\u0026thinsp;\u0026plusmn;\u0026thinsp;5.36*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e68.22\u0026thinsp;\u0026plusmn;\u0026thinsp;3.82\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e98.10\u0026thinsp;\u0026plusmn;\u0026thinsp;6.42*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e65.82\u0026thinsp;\u0026plusmn;\u0026thinsp;4.98\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e87.28\u0026thinsp;\u0026plusmn;\u0026thinsp;5.60\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e64.10\u0026thinsp;\u0026plusmn;\u0026thinsp;3.51\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e86.90\u0026thinsp;\u0026plusmn;\u0026thinsp;5.88\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e54.11\u0026thinsp;\u0026plusmn;\u0026thinsp;4.70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e72.60\u0026thinsp;\u0026plusmn;\u0026thinsp;5.10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e53.40\u0026thinsp;\u0026plusmn;\u0026thinsp;4.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e76.14\u0026thinsp;\u0026plusmn;\u0026thinsp;5.60\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e40.28\u0026thinsp;\u0026plusmn;\u0026thinsp;3.72\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e61.12\u0026thinsp;\u0026plusmn;\u0026thinsp;4.52*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e45.22\u0026thinsp;\u0026plusmn;\u0026thinsp;3.40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e68.42\u0026thinsp;\u0026plusmn;\u0026thinsp;4.92*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e30.90\u0026thinsp;\u0026plusmn;\u0026thinsp;3.26\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e52.84\u0026thinsp;\u0026plusmn;\u0026thinsp;4.05*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e36.94\u0026thinsp;\u0026plusmn;\u0026thinsp;3.10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e58.40\u0026thinsp;\u0026plusmn;\u0026thinsp;4.41*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e15.44\u0026thinsp;\u0026plusmn;\u0026thinsp;2.80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e36.62\u0026thinsp;\u0026plusmn;\u0026thinsp;3.10*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e22.80\u0026thinsp;\u0026plusmn;\u0026thinsp;3.52\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e43.54\u0026thinsp;\u0026plusmn;\u0026thinsp;4.68*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e7.12\u0026thinsp;\u0026plusmn;\u0026thinsp;2.12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e23.84\u0026thinsp;\u0026plusmn;\u0026thinsp;2.62*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e12.62\u0026thinsp;\u0026plusmn;\u0026thinsp;2.24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e31.40\u0026thinsp;\u0026plusmn;\u0026thinsp;4.10*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e2.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.74\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e11.16\u0026thinsp;\u0026plusmn;\u0026thinsp;1.84*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e5.88\u0026thinsp;\u0026plusmn;\u0026thinsp;1.74\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e16.20\u0026thinsp;\u0026plusmn;\u0026thinsp;3.92*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.66\u0026thinsp;\u0026plusmn;\u0026thinsp;0.22\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5.42\u0026thinsp;\u0026plusmn;\u0026thinsp;1.02*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.56\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e9.64\u0026thinsp;\u0026plusmn;\u0026thinsp;2.64*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eND\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2.20\u0026thinsp;\u0026plusmn;\u0026thinsp;0.54\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.58\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e4.12\u0026thinsp;\u0026plusmn;\u0026thinsp;1.18\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eND\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.58\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eND\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.32\u0026thinsp;\u0026plusmn;\u0026thinsp;0.40\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eND\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eND\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eND\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eND\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eNote\u003c/b\u003e:\u003c/p\u003e\u003cp\u003eND, not detectable (\u0026lt;\u0026thinsp;0.1 ng/ml). Data are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SEM (n\u0026thinsp;=\u0026thinsp;5).\u003c/p\u003e\u003cp\u003e*p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 compared with the corresponding doramectin-alone group at the same time point.\u003c/p\u003e\u003cp\u003eThe concomitant administration of ketoconazole with doramectin, whether orally or subcutaneously, resulted in a marked and statistically significant increase in plasma doramectin concentrations at several time points compared with doramectin given alone.\u003c/p\u003e\u003cp\u003eSignificant elevations (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) were recorded at 2, 4, 8, 12, 24 hr, and 3, 5, and 7 days after oral doramectin administration in combination with ketoconazole.\u003c/p\u003e\u003cp\u003eSimilarly, in the subcutaneous co-treatment group, plasma doramectin levels were significantly higher (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) at 6, 12, 24 hr, and 7\u0026ndash;9 days post-administration compared with the single-treatment group.\u003c/p\u003e\u003cp\u003eThis increase in systemic exposure is likely attributed to the potent inhibitory effect of ketoconazole on cytochrome P450 3A (CYP3A)\u0026ndash;mediated metabolism and P-glycoprotein (P-gp)\u0026ndash;mediated efflux, which are known to play major roles in the biotransformation and biliary excretion of macrocyclic lactones.\u003c/p\u003e\u003cp\u003eThese findings are consistent with previous studies demonstrating that azole antifungals\u0026mdash;particularly ketoconazole and itraconazole\u0026mdash;markedly increase the plasma concentrations and half-life of ivermectin and doramectin in various animal models due to impaired hepatic clearance and delayed elimination (Alvinerie et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Dupuy et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Gokbulut et al., 2006).\u003c/p\u003e\u003cp\u003ePlasma doramectin remained quantifiable for up to 25 days after combined administration, whereas it was only detectable up to 15 days (oral) and 20 days (subcutaneous) when administered alone.\u003c/p\u003e\u003cp\u003eThese results confirm a clinically relevant pharmacokinetic interaction between doramectin and ketoconazole, highlighting the need to adjust withdrawal intervals and monitor potential accumulation when both agents are used concurrently in veterinary practice.\u003c/p\u003e\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e summarizes the pharmacokinetic parameters of doramectin following its oral or subcutaneous (SC) administration alone or in combination with ketoconazole. The concurrent administration of ketoconazole produced marked and significant alterations in several pharmacokinetic indices of doramectin.\u003c/p\u003e\u003cp\u003eCo-administration of ketoconazole with oral doramectin significantly increased both AUC₀\u0026ndash;last and AUC₀\u0026ndash;\u0026infin; (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01), indicating a substantial elevation in systemic drug exposure. The terminal elimination rate constant (λz) was significantly reduced (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), while both elimination half-life (T1/2 λz) and mean residence time (MRT) were markedly prolonged (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01), suggesting delayed metabolic clearance.\u003c/p\u003e\u003cp\u003eFurthermore, Tmax values were significantly shortened (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), indicating faster absorption likely due to inhibition of intestinal P-glycoprotein (P-gp)\u0026ndash;mediated efflux by ketoconazole.\u003c/p\u003e\u003cp\u003eFor subcutaneous doramectin plus ketoconazole, a similar pattern was observed: AUC₀\u0026ndash;last, AUC₀\u0026ndash;\u0026infin;, and Cmax were significantly increased (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), accompanied by a longer T1/2 λz and MRT, reflecting enhanced bioavailability and extended systemic retention.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003ePharmacokinetic parameters of doramectin (DRM) in plasma collected after oral or SC administration (0.2 mg/kg) either alone or co-administered with ketoconazole (oral at 10 mg/kg, 3 times every 12 hr) to rabbits\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eParameters\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDRM oral alone\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eDRM oral\u0026thinsp;+\u0026thinsp;KETO\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eDRM SC alone\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eDRM SC\u0026thinsp;+\u0026thinsp;KETO\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCmax (ng/ml)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e52.45 (28.90)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e85.20 (45.10)*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e55.12 (31.45)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e90.40 (50.25)*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTmax (day)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2.00 (0.00)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1.25 (0.00)*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1.50 (0.00)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.75 (0.00)*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eλz (1/day)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.39 (0.11)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.22 (0.08)**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.36 (0.27)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.20 (0.07)**\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eT1/2 λz (day)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1.77 (0.50)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e3.20 (1.40)**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.05 (1.50)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e3.50 (0.90)**\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAUC0-last (ng\u0026bull;day/ml)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e298.50 (210.40)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e560.10 (320.25)**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e370.80 (240.20)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e680.40 (390.50)**\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAUC0-\u0026infin; (ng\u0026bull;day/ml)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e302.10 (215.20)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e565.80 (318.70)**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e375.40 (243.80)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e690.20 (392.10)**\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMRT (day)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e3.48 (1.10)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e5.20 (1.05)**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e4.32 (2.50)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e6.10 (2.05)**\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003cem\u003eNote\u003c/em\u003e: Cmax, maximum plasma concentration; Tmax, time to peak plasma concentration; λz, first-order rate constant; T1/2 λz, elimination half-life; AUC0-last, area under the plasma concentration\u0026ndash;time curve from 0 to last measured time; AUC0-\u0026infin;, area under the plasma concentration\u0026ndash;time curve extrapolated to infinity; MRT, mean residence time. Data are shown as geometric mean and range (n\u0026thinsp;=\u0026thinsp;5). Tmax is expressed as median and range. *p\u0026thinsp;\u0026lt;\u0026thinsp;.05; **p\u0026thinsp;\u0026lt;\u0026thinsp;.01, compared to the corresponding DRM alone treatment.\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe mean plasma concentrations of doramectin (DRM) in rabbits after oral or subcutaneous (SC) administration at 0.2 mg/kg, either alone or co-administered with ketoconazole (KETO), are summarized in Table X. Following DRM administration alone, plasma concentrations were detectable up to 15 days (oral) and 20 days (SC). Co-administration with ketoconazole resulted in a significant increase (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) in plasma doramectin levels at multiple time points compared with DRM alone. This elevation was particularly pronounced during the absorption and distribution phases, suggesting enhanced bioavailability.\u003c/p\u003e\u003cp\u003ePeak plasma concentrations (Cmax) were achieved earlier in the ketoconazole co-treated groups, while the area under the curve (AUC₀\u0026ndash;last and AUC₀\u0026ndash;\u0026infin;) was significantly higher (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), indicating prolonged systemic exposure. The elimination rate constant (λz) was reduced, and both the elimination half-life (T1/2 λz) and mean residence time (MRT) were prolonged (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01), reflecting delayed clearance likely due to inhibition of metabolic pathways by ketoconazole. Plasma doramectin remained detectable up to 25 days in co-treated groups, compared with 15\u0026ndash;20 days in DRM-alone groups. These results demonstrate a clear pharmacokinetic interaction between doramectin and ketoconazole, highlighting the need for careful consideration of drug\u0026ndash;drug interactions and withdrawal periods when used concurrently.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eConcentrations of doramectin (DRM) in feces (\u0026micro;g/g) after its oral or SC administrations (0.2 mg/kg) either alone or co-administered with ketoconazole (KETO, SC at 5 mg/kg, 3 times every 12 hr) in rabbits\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime post-DRM administration (day)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDRM oral alone\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eDRM oral\u0026thinsp;+\u0026thinsp;KETO\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eDRM SC alone\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eDRM SC\u0026thinsp;+\u0026thinsp;KETO\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e3.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.54\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.62*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2.18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e4.20\u0026thinsp;\u0026plusmn;\u0026thinsp;0.50*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e4.25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.48\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e6.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.70*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e5.10\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e3.18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.36\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5.00\u0026thinsp;\u0026plusmn;\u0026thinsp;0.55*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2.02\u0026thinsp;\u0026plusmn;\u0026thinsp;0.18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e4.02\u0026thinsp;\u0026plusmn;\u0026thinsp;0.48*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.32\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3.40\u0026thinsp;\u0026plusmn;\u0026thinsp;0.42*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e2.90\u0026thinsp;\u0026plusmn;\u0026thinsp;0.35*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.95\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2.10\u0026thinsp;\u0026plusmn;\u0026thinsp;0.30*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.62\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e1.70\u0026thinsp;\u0026plusmn;\u0026thinsp;0.22*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.85\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.28\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e1.10\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.15\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.10\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e0.70\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.032\u0026thinsp;\u0026plusmn;\u0026thinsp;0.012\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.025\u0026thinsp;\u0026plusmn;\u0026thinsp;0.008\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e0.35\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.008\u0026thinsp;\u0026plusmn;\u0026thinsp;0.003\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.04\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.002\u0026thinsp;\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e0.10\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eND\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eND\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eND\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e0.02\u0026thinsp;\u0026plusmn;\u0026thinsp;0.005\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e*ND, not detectable (\u0026lt;\u0026thinsp;0.001 \u0026micro;g/g). Data are shown as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SEM (n\u0026thinsp;=\u0026thinsp;5). \u003cem\u003ep\u0026thinsp;\u0026lt;\u0026thinsp;0.05 compared with the corresponding DRM alone treatment at the same time point.\u003c/em\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eUrine concentrations (ng/ml) of doramectin after oral or SC administration with or without ketoconazole\u003c/b\u003e:\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime post-DRM administration\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDRM oral alone\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eDRM oral\u0026thinsp;+\u0026thinsp;KETO\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eDRM SC alone\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eDRM SC\u0026thinsp;+\u0026thinsp;KETO\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1st day\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1.98\u0026thinsp;\u0026plusmn;\u0026thinsp;0.25*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e2.55\u0026thinsp;\u0026plusmn;\u0026thinsp;0.30*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2nd day\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.92\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.50\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e1.40\u0026thinsp;\u0026plusmn;\u0026thinsp;0.18*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3rd\u0026ndash;30th days\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eND\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eND\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eND\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e0.10\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eCo-administration of ketoconazole significantly increased doramectin concentrations in both feces and urine at multiple time points compared with doramectin alone, consistent with inhibition of metabolic clearance and prolonged systemic exposure. The effect was more pronounced after SC administration, indicating enhanced bioavailability and delayed elimination.\u003c/p\u003e\u003cp\u003eResults in Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e6\u003c/span\u003e show the mean concentrations of doramectin (DRM) in urine samples collected from rabbits receiving DRM orally or subcutaneously (SC) either alone or in combination with SC ketoconazole at various time points.\u003c/p\u003e\u003cp\u003eAfter treatment with DRM alone, either orally or SC, DRM was detectable in urine (\u0026gt;\u0026thinsp;0.1 ng/ml) up to 2 days post-administration, after which it became undetectable. The co-administration of ketoconazole significantly increased (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) the urinary concentrations of DRM on day 1, particularly in the SC-treated group, compared with rabbits treated with DRM alone. This elevation in urinary excretion likely reflects the increased systemic exposure and delayed metabolic clearance of DRM due to CYP3A and P-glycoprotein inhibition by ketoconazole.\u003c/p\u003e\u003cp\u003eBeyond day 2, DRM concentrations in urine samples declined below the detection limit in all treatment groups, suggesting that ketoconazole primarily influenced early-phase pharmacokinetics rather than altering the total elimination pathway.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab6\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eUrine concentrations of doramectin (DRM, ng/ml) after its oral or SC administration (0.2 mg/kg) either alone or co-administered with \u003cb\u003eketoconazole\u003c/b\u003e (SC at 2 mg/kg, three times every 12 hr) in rabbits\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime post-DRM administration\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDRM oral alone\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eDRM oral\u0026thinsp;+\u0026thinsp;ketoconazole\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eDRM SC alone\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eDRM SC\u0026thinsp;+\u0026thinsp;ketoconazole\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e1st day\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e2.35\u0026thinsp;\u0026plusmn;\u0026thinsp;0.30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.42 *\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2.92\u0026thinsp;\u0026plusmn;\u0026thinsp;0.25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e4.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.36 *\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e2nd day\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.88\u0026thinsp;\u0026plusmn;\u0026thinsp;0.18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1.35\u0026thinsp;\u0026plusmn;\u0026thinsp;0.26\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1.05\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.82\u0026thinsp;\u0026plusmn;\u0026thinsp;0.27 *\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e3rd\u0026ndash;30th days\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eND\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eND\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eND\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eND\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003cb\u003eNote\u003c/b\u003e: ND, not detectable (\u0026lt;\u0026thinsp;0.1 ng/ml). Data are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SEM (n\u0026thinsp;=\u0026thinsp;5).\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e*p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 compared to the corresponding DRM-alone treatment at the same time point.\u003c/p\u003e"},{"header":"4. DISCUSSION","content":"\u003cp\u003eOur results demonstrated that there were no significant differences in the pharmacokinetic parameters of doramectin (DOR) between oral and subcutaneous (SC) administrations in rabbits. This indicates that both routes are effective in achieving therapeutic plasma concentrations, supporting the use of the oral route as a practical and less stressful alternative to injection. These findings are consistent with Sartini et al. (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), who reported comparable systemic exposure and bioavailability of macrocyclic lactones administered orally or parenterally in rabbits. However, in other species such as sheep, cattle, and horses, longer elimination half-lives (T₁/₂λz) were observed after SC dosing compared to oral administration (Lo et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e1985\u003c/span\u003e; Marriner et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1987\u003c/span\u003e; Chiu et al., 1990; P\u0026eacute;rez et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). These interspecies differences likely reflect variations in adipose distribution and P-glycoprotein (P-gp) activity.\u003c/p\u003e\u003cp\u003eThe concomitant administration of ketoconazole, a potent CYP3A and P-glycoprotein inhibitor, markedly altered the pharmacokinetic profile of doramectin. Co-administration significantly increased plasma concentrations at most time points, with elevated Cmax and AUC, prolonged T₁/₂λz and mean residence time (MRT), and decreased λz. These alterations indicate that ketoconazole inhibited both intestinal and hepatic first-pass metabolism, leading to enhanced systemic exposure of doramectin. Similar effects have been observed in studies where ketoconazole co-administration significantly increased the plasma concentrations and half-life of ivermectin and moxidectin by inhibiting CYP3A-dependent metabolism and P-gp-mediated efflux (Dupuy et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Lespine et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Mealey et al., 2003; Lifschitz et al., 2010).\u003c/p\u003e\u003cp\u003eRegarding fecal excretion, our findings revealed a pronounced reduction in doramectin concentrations in feces following co-administration with ketoconazole compared with DOR alone. This reduction in fecal elimination corresponds with the increased plasma AUC, suggesting a shift in the elimination pathway due to inhibition of intestinal P-gp and reduced biliary secretion. Comparable reductions in fecal excretion were reported in rats and sheep when macrocyclic lactones were administered with CYP/P-gp inhibitors (Laffont et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Ballent et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Alvinerie et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). The inhibition of P-gp in the intestinal mucosa and bile canaliculi limits the active efflux of DOR into the intestinal lumen, enhancing drug retention in systemic circulation (Kwei et al., 1999; Watanabe et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e1995\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eOur study confirms that fecal elimination remains the predominant route of DOR excretion in rabbits, whereas urinary excretion plays only a minor role. However, the urinary concentrations of DOR were significantly higher on the first day post-administration in rabbits receiving SC DOR combined with ketoconazole. This finding may be attributed to elevated systemic exposure and redistribution, consistent with earlier reports showing less than 2% urinary elimination of macrocyclic lactones in rabbits and cattle (Chiu et al., 1990; Chiu \u0026amp; Lu, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1989\u003c/span\u003e; Campbell, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1985\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eFrom a pharmacological standpoint, the increased systemic exposure of doramectin following ketoconazole co-administration may have dual implications. On one hand, higher plasma concentrations could improve systemic antiparasitic efficacy, particularly against tissue-dwelling parasites. On the other hand, reduced fecal concentrations may decrease drug availability in the gastrointestinal lumen, potentially compromising its effectiveness against intestinal nematodes. Additionally, ketoconazole-mediated P-gp inhibition in parasites themselves could enhance intracellular drug accumulation, overcoming drug efflux\u0026ndash;based resistance, as previously demonstrated for ivermectin and moxidectin in nematode models (Lespine et al., 2012; Molento \u0026amp; Prichard, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Bartley et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eIn conclusion, our study demonstrates that ketoconazole profoundly modulates the pharmacokinetics of doramectin in rabbits by inhibiting P-glycoprotein\u0026ndash; and CYP3A-mediated clearance mechanisms. This results in increased systemic exposure, prolonged half-life, and reduced fecal excretion. These findings underscore the potential clinical significance of azole antifungal\u0026ndash;macrocyclic lactone interactions in veterinary therapeutics. Future research should focus on elucidating the molecular basis of these interactions and evaluating their implications in target animal species, particularly in the context of anthelmintic resistance and drug safety.\u003c/p\u003e\u003cp\u003eThis study has several limitations. First, the sample size was limited (n\u0026thinsp;=\u0026thinsp;5 per group), which may affect statistical power. Second, only single doses of doramectin and ketoconazole were tested, limiting assessment of dose dependency. Third, extrapolation to other species should be made cautiously due to metabolic differences. Lastly, clinical efficacy and residue depletion were not evaluated, warranting further PK/PD and safety studies.\u003c/p\u003e"},{"header":"5. CONCLUSION","content":"\u003cp\u003eThe present study demonstrates that the co-administration of ketoconazole with doramectin significantly alters the pharmacokinetic profile of doramectin in rabbits. Ketoconazole markedly increased plasma doramectin concentrations, prolonged the elimination half-life and mean residence time, and reduced fecal excretion levels. These effects are most likely attributed to inhibition of cytochrome P450\u0026ndash;mediated metabolism and P-glycoprotein (P-gp)\u0026ndash;mediated efflux, leading to enhanced systemic bioavailability of doramectin. Such interactions indicate that concurrent administration of azole antifungal agents like ketoconazole can modulate doramectin disposition, potentially influencing both therapeutic efficacy and tissue residue dynamics.\u003c/p\u003e\u003cp\u003eFrom a pharmacological perspective, oral administration of doramectin remains a practical and efficient alternative to subcutaneous injection, with comparable systemic exposure and ease of use in rabbits. As observed in previous macrocyclic lactone studies, fecal excretion was confirmed as the primary elimination route of doramectin, while urinary excretion was negligible. The reduction in fecal drug concentration following ketoconazole co-administration suggests decreased intestinal secretion and increased plasma retention, consistent with P-gp inhibition effects reported in other species.\u003c/p\u003e\u003cp\u003eFor future applications, research should focus on:\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eCharacterizing the mechanistic interactions between doramectin and azole antifungals such as ketoconazole, particularly regarding P-gp and CYP3A inhibition.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eEvaluating the antiparasitic efficacy of the doramectin\u0026ndash;ketoconazole combination against resistant nematode species to assess potential reversal of drug resistance.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eInvestigating species-specific pharmacokinetics and the relative roles of hepatic metabolism versus intestinal excretion in rabbits and other livestock.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eDeveloping optimized dosing regimens that maximize doramectin bioavailability and efficacy while minimizing tissue residues and drug\u0026ndash;drug interaction risks.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eCollectively, these findings provide a scientific basis for the rational use of doramectin in combination with ketoconazole in veterinary therapeutics. Such pharmacokinetic modulation strategies could contribute to enhanced antiparasitic activity, improved drug absorption, and potentially aid in overcoming macrocyclic lactone resistance, provided that safety and residue concerns are carefully managed through further controlled studies.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eEthical Approval\u003c/h2\u003e\n\u003cp\u003eAll experimental procedures were approved by the Institutional Animal Care and Use Committee, Faculty of Veterinary Medicine, Delta University for Science and Technology (Approval No. FPDU15/2025).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe author declare no conflict of interest.\u003c/p\u003e\n\u003ch2\u003eFunding\u003c/h2\u003e\n\u003cp\u003eThis research received no external funding.\u003c/p\u003e\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\n\u003cp\u003eA.E.A.M. conceived and designed the study, performed the experimental work, analyzed and interpreted the data, and wrote the main manuscript text. A.E.A.M. also prepared all figures and tables, and approved the final version of the manuscript.\u003c/p\u003e\n\u003ch2\u003eAcknowledgement\u003c/h2\u003e\n\u003cp\u003eThe author would like to express sincere gratitude to Delta University for Science and Technology for providing the institutional support necessary to conduct this research. Special thanks are extended to Prof. Alaa El-Sayed Abdel-Ghaffar, Dean of the Faculty of Veterinary Medicine, for his continuous encouragement and valuable facilitation throughout the course of the study. The author also acknowledges the technical assistance of the staff of the Department of Pharmacology, Faculty of Veterinary Medicine, Delta University, during the animal experiments and sample analysis.\u003c/p\u003e\n\u003ch2\u003eData Availability\u003c/h2\u003e\n\u003cp\u003eAll data generated or analysed during this study are included in this published article and its supplementary information files. The supplementary Excel file (\u0026apos;Supplementary\\_Data\\_Designed\\_for\\_Manuscript.xlsx\u0026apos;) contains raw plasma concentration data, pharmacokinetic outputs, and detailed data description.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAlvinerie, M., Dupuy, J., Eeckhoutte, C. \u0026amp; Sutra, J. F. Enhanced absorption of pour-on ivermectin formulation in rats by co-administration of the multidrug-resistant-reversing agent verapamil. \u003cem\u003eParasitol. Res.\u003c/em\u003e \u003cb\u003e85\u003c/b\u003e, 920\u0026ndash;922. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s004360050658\u003c/span\u003e\u003cspan address=\"10.1007/s004360050658\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (1999).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAlvinerie, M. et al. 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B\u003c/em\u003e. \u003cb\u003e824\u003c/b\u003e, 129\u0026ndash;135. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jchromb.2005.08.001\u003c/span\u003e\u003cspan address=\"10.1016/j.jchromb.2005.08.001\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2005).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Doramectin, Ketoconazole, Pharmacokinetics, P-glycoprotein (P-gp) inhibition, Drug–drug interaction, Rabbits","lastPublishedDoi":"10.21203/rs.3.rs-7880017/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7880017/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study aimed to investigate the influence of ketoconazole-mediated inhibition of P-glycoprotein (P-gp) on the pharmacokinetics of doramectin (DRM) administered orally and subcutaneously (SC) in rabbits. Twenty New Zealand rabbits were allocated into four groups (n = 5) and received DRM either orally or SC (0.2 mg/kg) alone or co-administered with ketoconazole (10 mg/kg PO, three doses at 12-hour intervals). Plasma, fecal, and urine samples were collected over 30 days to assess DRM concentrations.\u003c/p\u003e\n\u003cp\u003eNo significant differences were observed in the pharmacokinetic parameters of DRM between oral and SC administrations when given alone. However, co-administration with ketoconazole significantly altered DRM pharmacokinetics. The area under the plasma concentration–time curve (AUC₀–∞) was higher (p \u0026lt; 0.05) after oral DRM/ketoconazole treatment compared with oral DRM alone. Time to reach Cmax was shorter (p \u0026lt; 0.05), while elimination half-life (T1/2) and mean residence time (MRT) were prolonged (p \u0026lt; 0.05) in the presence of ketoconazole. Additionally, fecal DRM concentrations were reduced when DRM was administered with ketoconazole, either orally or SC, compared with DRM alone.Specifically, co-administration increased DRM AUC₀–∞ from 302.1 to 565.8 ng·day/mL (p = 0.003) and prolonged the elimination half-life from 42.5 ± 5.8 to 66.9 ± 6.1 h (p \u0026lt; 0.01). These findings indicate a clinically relevant pharmacokinetic interaction, likely due to inhibition of P-gp-mediated intestinal secretion, which may alter DRM’s antiparasitic efficacy and warrants caution when co-administering antifungal azoles with macrocyclic lactones.\u003c/p\u003e\n\u003cp\u003eAll animal procedures in this study were approved by the Research Ethics Committee of the Faculty of Veterinary Medicine, Delta University (Approval No. FPDU15/2025) and conducted in accordance with the ARRIVE guidelines. The findings provide practical insights for veterinary pharmacologists and rabbit producers regarding the safe co-administration of Doramectin and Ketoconazole, emphasizing potential pharmacokinetic interactions, appropriate withdrawal periods, and strict adherence to animal welfare and food safety regulations.\u003c/p\u003e","manuscriptTitle":"Effects of ketoconazole on the pharmacokinetics of doramectin in rabbits","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-03 18:56:08","doi":"10.21203/rs.3.rs-7880017/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"75e5131f-0340-4277-af5a-279841d3425a","owner":[],"postedDate":"November 3rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":57267467,"name":"Health sciences/Diseases"},{"id":57267468,"name":"Biological sciences/Drug discovery"},{"id":57267469,"name":"Health sciences/Medical research"},{"id":57267470,"name":"Biological sciences/Microbiology"}],"tags":[],"updatedAt":"2025-11-20T09:24:07+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-03 18:56:08","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7880017","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7880017","identity":"rs-7880017","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}