Elevated neutrophil-to-lymphocyte ratios correlate with increased clozapine concentration-to-dose ratios during titration

Elevated neutrophil-to-lymphocyte ratios correlate with increased clozapine concentration-to-dose ratios during titration | 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 Elevated neutrophil-to-lymphocyte ratios correlate with increased clozapine concentration-to-dose ratios during titration Yuki Kikuchi, Bunichiro Onodera, Mutsumi Sakata, Kazuro Ikawa, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6460947/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 10 Jul, 2025 Read the published version in Schizophrenia → Version 1 posted You are reading this latest preprint version Abstract Few cohort studies have examined the relationship between inflammation and increased clozapine blood levels. The purpose of this study was to investigate the relationship between the neutrophil-to-lymphocyte ratio (NLR), a marker of inflammation, and the clozapine concentration-to-dose (C/D) ratio during clozapine titration. We retrospectively investigated the medical records of all patients at Nozoe Hills Hospital who met the following criteria: 1) patients with schizophrenia who were first treated with clozapine between April 2020 and July 2024 and 2) patients for whom clozapine blood levels were measured for at least two consecutive weeks after the start of clozapine treatment. The study included 143 blood samples from 28 patients collected within 6 weeks of starting clozapine treatment. A linear mixed model with random intercepts was used to determine the correlation between the clozapine C/D ratio and NLR in samples repeatedly measured within an individual. Fixed effects for the C/D ratio included NLR, week, and the interaction between NLR and week. A significant fixed effect of NLR on C/D ratio was observed (estimate: 0.70; 95% confidence interval: 0.47–0.92; P<0.0001). The fixed effect of NLR was attenuated over time due to a significant negative interaction between NLR and week. The fixed effect of NLR remained significant even after excluding the six patients who had fever during clozapine titration. This study suggests a positive correlation between the C/D ratio and NLR during clozapine titration. Our findings indicate that subclinical inflammation in the early titration phase affects the pharmacokinetics of clozapine. Health sciences/Biomarkers Biological sciences/Drug discovery/Pharmacology C-reactive protein drug monitoring fever inflammation precision medicine Figures Figure 1 Figure 2 1 Introduction Clozapine is a highly effective atypical antipsychotic used for the management of treatment-resistant schizophrenia; however, it is underused because of its various side effects. The ability to metabolize clozapine varies significantly among individuals. 1 , 2 Factors such as sex, smoking, and ethnicity are known to affect clozapine metabolism, and international guidelines recommend initial titration protocols that consider these factors. 1 Rapid clozapine titration that is not appropriate for an individual's metabolic capacity can lead to early inflammatory side effects such as fever, myocarditis, and pneumonia. 3 – 6 This may progress to a life-threatening condition characterized by organ damage such as myocarditis, pneumonia, nephritis, liver dysfunction, and pancreatitis, which may be accompanied by eosinophilia and rash, and is diagnosed as clozapine-associated drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome. 7 – 9 These conditions are thought to be caused by an immune hypersensitivity reaction to clozapine. The relative mortality rate of myocarditis and pneumonia associated with clozapine is significantly higher than that of clozapine-associated agranulocytosis. 10 , 11 Therefore, it is important to estimate the clozapine-metabolizing ability of an individual early in the titration phase and perform individualized titration. Measuring the clozapine concentration-to-dose (C/D) ratio helps estimate the individual metabolic capacity. Our previous study analyzing the weekly measurements of clozapine blood concentrations within 6 weeks of starting clozapine revealed that fever increased the clozapine C/D ratio. 12 Inflammation reportedly reduces the activity of cytochrome P450 (CYP) 1A2, the main enzyme involved in the metabolism of clozapine. 13 The underlying mechanism is hypothesized to be that inflammatory cytokines such as interleukin-6 and tumor necrosis factor-α suppress the transcription of CYP1A2, thereby reducing its synthesis and activity. 14 , 15 The inflammation induced by clozapine itself may impair its metabolism, leading to increased clozapine blood levels and further inflammation, creating a vicious cycle. 16 Therefore, international guidelines recommend measuring C-reactive protein (CRP) weekly for the first 4 weeks after initiating clozapine and avoiding dose increases if CRP levels rise. 1 Our previous study measured CRP levels weekly or daily during clozapine titration and reported that CRP levels were elevated in many patients even in the absence of obvious inflammatory symptoms such as fever. 17 Furthermore, we showed that the C/D ratio may temporarily increase even in patients without fever. 12 Based on these results, we hypothesized that subclinical inflammation during clozapine titration increases the clozapine C/D ratio. Most of the data on the relationship between inflammation and elevated blood clozapine levels is based on case reports, and studies with well-controlled cohorts are lacking. 18 , 19 A recent retrospective study by Smith et al. identified 126 patients who had their clozapine blood levels and CRP levels measured simultaneously, demonstrating an association between CRP and clozapine blood levels. 20 However, they were limited as the clinical context of each patient and the timing of the blood measurements (number of days after starting clozapine) were unknown, and the longitudinal change in the C/D ratio within patients was unknown. 21 Therefore, we decided to examine the relationship between inflammation and clozapine blood levels using past datasets. Although CRP was not measured simultaneously with clozapine blood levels, neutrophil and lymphocyte counts were routinely measured in clinical practice. We therefore decided to use the neutrophil/lymphocyte ratio (NLR) as a marker of inflammation. NLR is a readily available, robust biomarker of inflammation, stress, and immune system activation that was proposed by Zahorec more than 20 years ago. 22 , 23 NLR is widely used in general internal medicine (inflammation and infection), intensive care medicine, oncology, surgery, and perioperative medicine, and has been established as a very sensitive marker of inflammation and stress. 23 It is also used to assess inflammation in chronic diseases, including diabetes, cancer, ischemic heart disease, and psychiatric disorders. 23 There is growing evidence suggesting that inflammation may be involved in the pathogenesis and prognosis of psychiatric disorders 24 , 25 and NLR is extensively used as an indicator of inflammation in psychiatric research. 26 Thus, the present study aimed to investigate whether an increase in NLR, an alternative marker of inflammation, 22 , 23 would be associated with an increase in the C/D ratio upon reanalyzing the dataset of our previous publication, 12 in which the blood concentration of clozapine and the number of neutrophils and lymphocytes were measured simultaneously every week for 6 weeks from the start of treatment. 2 Methods 2.1 Study participants The present study is a reanalysis of data from our previous publication, in which clozapine levels were measured weekly for 6 weeks after starting treatment. 12 This study is a secondary analysis of this dataset. Briefly, we retrospectively investigated the medical records of all patients at Nozoe Hills Hospital who met the following criteria: 1) patients with schizophrenia who were first treated with clozapine between April 2020 and July 2024 and 2) patients for whom clozapine blood levels were measured for at least two consecutive weeks after the start of clozapine treatment. Schizophrenia was diagnosed based on the International Classification of Diseases, 10th revision. Because this retrospective study used anonymized data, an opt-out form was displayed on the hospital’s bulletin board before data collection. Individuals who did not express their intent for exclusion were included in the study. This study was approved by the Ethics Committee of Nozoe Hills Hospital (Approval ID: 2024-6). 2.2 Measurement of clozapine blood levels All blood concentration measurements were performed in an inpatient setting and the vital signs and medication adherence of the patients were monitored by a nurse. Smoking was prohibited at the hospital. The details of concomitant medications at the start of clozapine treatment have been described previously, 12 and there was no concomitant use of potent CYP1A2 inhibitors. Blood clozapine levels within 6 weeks of starting clozapine treatment were included in this study. Clozapine levels were measured simultaneously with weekly blood tests for white blood cell and neutrophil counts, as required in Japan, after starting clozapine. In most patients, blood was collected approximately 12 h after the last clozapine dose. Blood clozapine levels were measured by high-performance liquid chromatography at the Department of Clinical Pharmacotherapy, Hiroshima University, Hiroshima, Japan, as previously reported. 12 Blood clozapine levels measured while the temperature of the patient exceeded 38℃ until it dropped below 37℃ were classified as measurements taken during fever. 2.3 Assessment of C/D ratio and NLR The average clozapine dose up to 5 days before the blood clozapine level measurements was used to calculate the C/D ratios for each patient. This is because the clozapine dose changed during titration, and steady-state blood concentration measurements were not available. Generally, approximately 95% of the steady-state concentration is achieved in five half-lives, and 99% is achieved in seven half-lives. 27 Assuming a half-life of 24 h for repeated doses of clozapine, a steady state can be achieved in five days. 28 The NLR or neutrophil counts/lymphocyte counts were calculated simultaneously with the blood clozapine concentration measurement. 2.4 Statistical analysis Statistical analyses were performed using the EZR software (Jichi Medical University, Saitama, Japan). First, to roughly estimate the overall correlation, Pearson's product-moment correlation coefficient was calculated for all samples for the correlation between C/D ratio and NLR, C/D ratio and neutrophil counts, and C/D ratio and lymphocyte counts. Next, a linear mixed model with restricted maximum likelihood estimation was used to clarify the correlation between the C/D ratio and NLR in samples that were repeatedly measured within individuals. The fixed effects used to estimate the C/D ratio included the NLR (continuous variable), week (continuous variable), and the interaction between the NLR and week. We also analyzed sex, obesity (body mass index [BMI] > 30), concomitant valproate use, and smoking before hospitalization as covariates in a linear mixed model as a sensitivity analysis. The random effects considered the individual variability of the intercept. Because the C/D ratio and NLR were not normally distributed, they were transformed to the natural logarithm. We performed a sensitivity analysis, excluding six patients who developed fever within 6 weeks after starting clozapine treatment. The statistical significance level was set at P < 0.05. 3 Results A total of 28 patients were included in the study. There were 143 clozapine blood samples measured weekly within 6 weeks of clozapine initiation. Detailed patient demographics and clozapine blood concentration data are shown in Table 1. Of the 28 patients, six had fever within 6 weeks of clozapine initiation, but only three blood clozapine samples were measured during fever. In all 143 samples, the median C/D ratio (interquartile range [IQR]) was 1.43 (1.05–2.0), and the median NLR (IQR) was 1.85 (1.43–2.79). Table 2 shows ranges of C/D ratios and NLRs by week. Although we have previously reported weekly C/D ratios using the same cohort, 12 the present study describes a more detailed range. From weeks 1 to 3, the median NLR was significantly higher in patients with fever than in those without (Table 2). As we reported previously, 12 in weeks 1 and 2, the median C/D ratio was significantly higher in patients with fever than in those without (Table 2). Pearson’s product-moment correlation analysis indicated a significant correlation between the C/D ratio and neutrophil count (correlation coefficient = 0.255, 95% confidence interval [CI]: 0.0952–0.403, P < 0.005), as shown in Fig. 1(a). In contrast, a significant negative correlation was shown between the C/D ratio and lymphocyte count (correlation coefficient = −0.195, 95% CI: −0.348 to −0.0323, P < 0.05) (Fig. 1(b)). Among these analyses, the correlation between the C/D ratio and NLR was the strongest (correlation coefficient = 0.37, 95% CI: 0.22 to 0.504, P < 0.00001) (Fig. 1(c)). Next, we used a linear mixed model to examine the fixed effect of NLR on the C/D ratio in repeatedly measured samples within individuals. A significant fixed effect of NLR on C/D ratio was observed (estimate: 0.70; 95% CI: 0.47 to 0.92; P < 0.0001) (Table 3). Since we found significant interactions between NLR and week, we calculated an estimate of the fixed effect of NLR on the C/D ratio with the week interaction considered (Fig. 2(a)). The fixed effect of NLR was attenuated over time due to a significant negative interaction between NLR and week. (Fig. 2(a)). As a sensitivity analysis, the same analysis was performed excluding the six patients who had fever within 6 weeks after starting clozapine treatment. The results of the sensitivity analysis were generally consistent with those of the main analysis (Table 4, Fig. 2(b)). We also performed a sensitivity analysis by including sex, obesity (BMI > 30), concomitant use of valproic acid, and smoking before hospitalization as covariates in a linear mixed model, but no significant effect was observed for any of these factors (Supplementary Tables 1-4). 4 Discussion The present study's main finding was identifying a positive correlation between NLR and C/D ratio during clozapine titration. Although the relationship between inflammation and increased blood clozapine levels has been demonstrated in numerous case reports, 18 only a few cohort studies have been conducted under well-controlled conditions. 19 In a cohort of 131 Chinese patients, 29 inflammation/infection was observed on 2% of the total monitored days (482/24,789), occurring in 18 episodes across 16 patients. Eleven percent of the infection episodes did not show any clinically relevant effect (no increase in white blood cells or CRP levels). In 61% of the infection episodes, it was recommended to reduce the clozapine dose by half, and in 28% of the infection episodes, it was recommended to reduce the clozapine dose by one-third. In a cohort of 65 hospitalized Chinese patients, 15 the clozapine C/D ratios during infection were significantly higher than at baseline, and a significant positive correlation was found between the C/D ratios and white blood cell and neutrophil counts. Recently, Smith et al. showed in a retrospective study of 126 patients that the C/D ratio was three times higher in non-smokers with high CRP levels (CRP > 50 mg/L) than in those with low CRP levels (CRP < 5 mg/L). 20 The strength of the current study is that blood clozapine levels and NLR were measured under well-controlled conditions every week for 6 weeks after clozapine initiation during hospitalization. Furthermore, even when the six patients who had fever during clozapine titration were excluded, a significant correlation was observed between the clozapine C/D ratio and the NLR, suggesting that blood clozapine levels increased when the NLR, a marker of inflammation, was high, even when the patient was clinically asymptomatic. The reference range for NLR is 1 to 2, and values higher than 3 are considered pathological. 30 The linear mixed model of this study showed that when the NLR increased by 1%, the C/D ratio increased by 0.70%. In weeks 1 to 3, the median NLR was significantly higher in patients with fever than in those without, exceeding 3, and the median C/D ratio was also significantly higher in patients with fever than in those without in weeks 1 and 2 (Table 2). Therefore, although no clear threshold for NLR was identified in the present study, the possibility of unexpectedly high blood levels of clozapine may be considered when the NLR exceeds 3. In addition, the present study showed that the fixed effect of NLR on the C/D ratio significantly decreased over time. This fact may suggest that subclinical inflammation is likely to occur early after the start of clozapine (weeks 1–3), i.e., the NLR and C/D ratio are likely to increase at this time. However, the frequency and onset time of inflammation may be affected by titration speed. 4 , 31 , 32 Our results suggest that subclinical inflammation during clozapine titration can increase blood clozapine levels more than expected and underscore the importance of CRP monitoring in detecting subclinical inflammation during clozapine titration. As international guidelines recommend measuring CRP and clozapine blood levels weekly after starting clozapine, 1 clinicians should monitor CRP and clozapine blood levels. 33 CRP levels were markedly higher than the reference range in all samples during fever (Table 1 ; n = 5). Considering that the median NLR was significantly higher in patients with fever than in those without (Table 2), CRP, NLR, and C/D ratio may be correlated. However, although CRP and NLR are both inflammatory biomarkers, there may be differences in the timing and degree of elevation between CRP and NLR, and further studies are needed regarding their clinical applicability. The results of this study show that clinicians can estimate inflammation and elevated clozapine blood levels using neutrophil and lymphocyte counts, which are routinely measured in clinical practice during clozapine titration. By monitoring CRP levels and NLR during clozapine titration, clinicians can detect subclinical inflammation early and take measures such as temporarily halting titration, thereby preventing the progression of clozapine-induced life-threatening conditions such as myocarditis, pneumonia, and DRESS syndrome. In this cohort, the median clozapine dose at week 4 was 75 mg/day, and the median clozapine blood level at week 4 was 116 ng/mL. In a study of 1,408 Korean inpatients, the average clozapine dose was approximately 200 mg/day after 4–8 weeks of initiation, and the average C/D ratio was 1.23 ng/mL per mg/day. 34 International guidelines recommend the slowest titration for non-smoking Asian women, with 175 mg/day for normal metabolizers and 75 mg/day for poor metabolizers at week 4 after starting clozapine. 35 Naturalistic observations may indicate that Asian populations tolerate clozapine at lower doses than European populations. This study has several limitations. First, the number of patients included was small. Further studies with larger sample sizes are needed to confirm our results. Second, it is difficult to use steady-state concentrations during titration; therefore, the average dose over the five days before measuring blood concentration was used to calculate the C/D ratio. However, since the participants in the present study were titrated very slowly (Table 1 ), 12 the clozapine dose remained almost unchanged over 5 days, and this limitation had little effect on our findings. Finally, this study was conducted entirely on Japanese patients; therefore, while it has the advantage of being a homogeneous ethnic group, it cannot be generalized to other populations. Japanese people belong to the East Asian ethnic group and have the lowest clozapine metabolism capacity among all ethnic groups. 1 , 2 International guidelines recommend the slowest titration speed for Japanese people. 1 The frequency of inflammatory side effects caused by clozapine is reported to be higher in Japanese people than in Europeans. 3 It cannot be ruled out that both clozapine metabolism capacity and immunological responsiveness to clozapine differ among ethnic groups. Therefore, future studies should clarify the relationship between clozapine titration and inflammation in other ethnic groups. In conclusion, this study suggests a positive correlation between the C/D ratio and NLR during clozapine titration. Our findings indicate that subclinical inflammation in the early titration phase affects the pharmacokinetics of clozapine. Declarations Data availability statement The data are not publicly available because they contain information that could compromise the research participants’ privacy/consent. Acknowledgements We would like to thank Editage (www.editage.jp) for the English language editing. Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Competing Interests The authors declare that this study was conducted in the absence of any commercial or financial relationships that could be construed as potential conflicts of interest. Author Contributions Bunichiro Onodera: Formal analysis, Writing - original draft. Mutsumi Sakata: Investigation, Writing - review & editing. Kazuro Ikawa: Investigation, Writing - review & editing. Daisuke Kume: Investigation, Writing - review & editing. Naoki Horikawa: Investigation, Writing - review & editing. Hiroshi Komatsu: Supervision, Writing - review & editing. Takuhiro Yamaguchi: Methodology, Formal analysis, Writing - Review & Editing. Hiroaki Tomita: Supervision, Writing - review & editing. Yuki Kikuchi: Conceptualization, Formal analysis, Methodology, Project administration, Writing - review & editing. References de Leon, J. et al. An international adult guideline for making clozapine titration safer by using six ancestry-based personalized dosing titrations, CRP, and clozapine levels. Pharmacopsychiatry 55 , 73–86 (2022). de Leon, J. et al. Letter to the FDA proposing major changes in the US clozapine package insert supported by clozapine experts worldwide. 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Tables Table 1: Patient characteristics and blood clozapine measurements Number of patients 28 Female, n (%) 15 (54) Age, year, mean (SD) 30.6 (16.1) BMI, kg/m 2 , mean (SD) 23.3 (5.2) Obesity (BMI>30), n (%) 3 (11) Smoking before starting clozapine, n (%) 1 4 (14) Concomitant valproate at clozapine initiation, n (%) 8 (29) Body temperature before starting clozapine, ℃, median (min, IQR, max) 36.4 (35.3, 36.2–36.6, 37.1) Patient with fever, n (%) 6 (21) Number of clozapine blood levels measured, n 143 Number of measurements during fever, n (%) 3 (2.1) CRP levels measured during fever, mg/dL, mean (SD) (n = 5) 8.61 (4.85) Clozapine dose, mg/day, median (min, IQR, max) 75 (25, 45–100, 300) Clozapine blood levels, ng/mL, median (min, IQR, max) 93 (13, 57–153.5, 626) C/D ratio, (ng/mL)/(mg/day), median (min, IQR, max) 1.43 (0.26, 1.05–2.0, 6.96) White blood cell count, ×10 3 /mm 3 , median (min, IQR, max) 6.02 (4.0, 5.20–7.68, 17.8) Neutrophil count, ×10 3 /mm 3 , median, (min, IQR, max) 3.42 (2.01, 2.61–4.65, 12.0) Lymphocyte count, ×10 3 /mm 3 , median (min, IQR, max) 1.91 (0.42, 1.43–2.33, 4.61) NLR, median (min, IQR, max) 1.85 (0.75, 1.42–2.79, 9.14) 1: Smoking was prohibited during clozapine titration. BMI, body mass index; C/D, concentration-to-dose; CRP, C-reactive protein; IQR, interquartile range; NLR, neutrophil-to-lymphocyte ratio; min, minimum; max; maximum Table 2: Ranges of weekly C/D ratios and NLRs C/D ratio, median (min, IQR, max) NLR, median (min, IQR, max) Patients with fever Patients without fever P 1 Patients with fever Patients without fever P 1 Week 1 (n =28) 2.12 (1.43, 1.87–3.06, 4.49) 1.31 (0.35, 0.94–1.88, 2.80) 0.022 3.16 (1.46, 2.32–4.53, 9.14) 1.31 (0.79, 1.14–1.56, 2.98) <0.001 Week 2 (n =28) 3.48 (1.68, 2.30–4.18, 6.96) 1.23 (0.35, 0.94–2.12, 2.82) 0.01 3.50 (2.04, 3.36–4.50, 7.36) 1.76 (0.75, 1.48–2.33, 5.34) <0.001 Week 3 (n =25) 2.80 (1.20, 1.60–4.20, 5.20) 1.32 (0.55, 1.14–1.67, 4.10) 0.11 4.57 (2.95, 3.74–4.57, 6.49) 1.86 (0.93, 1.21–2.22, 7.96) 0.0085 Week 4 (n =27) 1.12 (0.94, 1.07–1.83, 2.59) 1.33 (0.26, 1.03–1.73, 3.42) 0.93 3.17 (1.61, 3.14–5.86, 5.88) 1.89 (0.95, 1.45–2.45, 7.89) 0.055 Week 5 (n =18) 2.01 (1.12, 1.75–2.10, 2.27) 1.33 (0.43, 1.18–2.07, 2.76) 0.57 2.28 (1.61, 1.69–3.47, 5.38) 1.97 (0.94, 1.48–2.47, 4.95) 0.442 Week 6 (n =17) 1.49 (1.26, 1.38–2.12, 2.74) 1.32 (0.28, 1.02–1.59, 2.64) 0.31 1.87 (1.49, 1.68–3.44, 5.00) 1.61 (0.85, 1.20–3.31, 7.49) 0.59 1: The weekly C/D ratios and NLRs were compared between patients with and without fever using the Mann–Whitney U test. C/D, concentration-to-dose; IQR, interquartile range; NLR, neutrophil-to-lymphocyte ratio; min, minimum; max; maximum Table 3: Estimates of fixed effects on the C/D ratio in a linear mixed model (all patients) 95% confidence interval Estimate SE Lower limit Upper limit T value P NLR 0.70 0.12 0.47 0.92 6.13 < 0.0001 Week 0.02 0.02 −0.03 0.06 0.69 0.493 NLR × Week −0.10 0.03 −0.15 −0.04 −3.38 < 0.001 Note: Number of patients = 28; Number of blood samples = 143 The C/D ratio and NLR were converted to natural logarithms. C/D, concentration-to-dose; NLR, neutrophil-to-lymphocyte ratio; SE, standard error Table 4: Estimates of fixed effects on the C/D ratio in a linear mixed model (excluding the six patients with fever) 95% CI Estimate SE Lower limit Upper limit T value P NLR 0.53 0.14 0.26 0.79 3.89 < 0.001 Week 0.02 0.02 −0.02 0.06 0.84 0.40 NLR × Week −0.07 0.03 −0.14 −0.01 −2.29 0.024 Note: Number of patients = 22; Number of blood samples = 115 The C/D ratio and NLR were converted to natural logarithms. C/D, concentration-to-dose; NLR, neutrophil-to-lymphocyte ratio; SE, standard error Additional Declarations There is no conflict of interest Supplementary Files SupplementaryTablesR2.docx Supplementary Tables 1-4 Cite Share Download PDF Status: Published Journal Publication published 10 Jul, 2025 Read the published version in Schizophrenia → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6460947","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":474436318,"identity":"2e4a38a1-ba3f-488a-863a-0d3b13f5f50a","order_by":0,"name":"Yuki Kikuchi","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA70lEQVRIiWNgGAWjYDACHsZmIHmAhx/MQQgToUWygXgtDMwgLQwGBwgohAODM4ebjXlq7sgYnz/87MEbBht5cwbegw8YZO7g1nK2sTmZ59gzHrMbaeaGcxjSDHc28CUbMPA8w63lPGPzYd6Gw0AtDGbSPAyHEwwO8JhJMPAcJqzFuP/4N5gW8x94tYAcBtJiwJCDsIUBnxbJMwebDeccO8wjcSOnTHKOQZrhBqCNEgl4/MJ3Jv2xxJuaw/b8/ce3SbypsJE3ON5j+OFjD+4QUziA6k4gBsVTYs8BLIohQL4Bu/gP3FpGwSgYBaNgxAEApAFTL1altyMAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0002-1184-8918","institution":"Tohoku University, Graduate School of Medicine","correspondingAuthor":true,"prefix":"","firstName":"Yuki","middleName":"","lastName":"Kikuchi","suffix":""},{"id":474436319,"identity":"98a17bef-c1ad-4e73-bf44-2fbea6dfe4cb","order_by":1,"name":"Bunichiro Onodera","email":"","orcid":"","institution":"Tohoku University, Graduate School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Bunichiro","middleName":"","lastName":"Onodera","suffix":""},{"id":474436320,"identity":"f1057ceb-bec8-4430-ac1a-618a9eeb6adf","order_by":2,"name":"Mutsumi Sakata","email":"","orcid":"","institution":"Nozoe Hills Hospital","correspondingAuthor":false,"prefix":"","firstName":"Mutsumi","middleName":"","lastName":"Sakata","suffix":""},{"id":474436321,"identity":"604e28c7-9a9b-4d90-9c24-3a028c127f4a","order_by":3,"name":"Kazuro Ikawa","email":"","orcid":"https://orcid.org/0000-0002-9349-4067","institution":"Hiroshima University","correspondingAuthor":false,"prefix":"","firstName":"Kazuro","middleName":"","lastName":"Ikawa","suffix":""},{"id":474436322,"identity":"22406c99-8ebc-4319-b46f-e315ea445586","order_by":4,"name":"Daisuke Kume","email":"","orcid":"https://orcid.org/0009-0005-4861-5957","institution":"Nozoe Hills Hospital","correspondingAuthor":false,"prefix":"","firstName":"Daisuke","middleName":"","lastName":"Kume","suffix":""},{"id":474436323,"identity":"d7e07925-2c70-49dd-9b8e-89f40334dca8","order_by":5,"name":"Naoki Horikawa","email":"","orcid":"https://orcid.org/0009-0009-9646-5278","institution":"Nozoe Hills Hospital","correspondingAuthor":false,"prefix":"","firstName":"Naoki","middleName":"","lastName":"Horikawa","suffix":""},{"id":474436324,"identity":"9d515723-f451-40dd-9903-377061908ecb","order_by":6,"name":"Hiroshi Komatsu","email":"","orcid":"","institution":"Tohoku University Hospital","correspondingAuthor":false,"prefix":"","firstName":"Hiroshi","middleName":"","lastName":"Komatsu","suffix":""},{"id":474436325,"identity":"bfedc269-d9fe-4a1e-861e-42520b2189c7","order_by":7,"name":"Takuhiro Yamaguchi","email":"","orcid":"","institution":"Tohoku University Graduate School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Takuhiro","middleName":"","lastName":"Yamaguchi","suffix":""},{"id":474436326,"identity":"1d097c0c-1be1-4e68-b1af-02fbebdb0a78","order_by":8,"name":"Hiroaki Tomita","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Hiroaki","middleName":"","lastName":"Tomita","suffix":""}],"badges":[],"createdAt":"2025-04-16 07:55:52","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6460947/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6460947/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41537-025-00648-4","type":"published","date":"2025-07-10T04:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":85744680,"identity":"027a4007-d373-458c-8397-e73eb27b6075","added_by":"auto","created_at":"2025-07-01 09:18:24","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":97393,"visible":true,"origin":"","legend":"\u003cp\u003ePearson’s correlation coefficients for (a) C/D ratio and neutrophil count, (b) C/D ratio and lymphocyte count, and (c) C/D ratio and NLR. The shaded area indicates the confidence interval at the 95% confidence level.\u003c/p\u003e\n\u003cp\u003eC/D ratio, concentration-to-dose ratio; NLR, neutrophil-to-lymphocyte ratio.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6460947/v1/27b24dd92fccca3c4fa9ca91.png"},{"id":85746124,"identity":"8080c724-db00-4852-9320-0fc57e707a0e","added_by":"auto","created_at":"2025-07-01 09:26:24","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":85358,"visible":true,"origin":"","legend":"\u003cp\u003eEstimates of the fixed effects of the NLR by week on the C/D ratio. (a) Analysis of all patients (28 patients, 143 samples). (b) Sensitivity analysis excluding the six patients who had fever within 6 weeks after starting clozapine treatment (22 patients, 115 samples). The shaded area indicates the confidence interval at the 95% confidence level.\u003c/p\u003e\n\u003cp\u003eC/D ratio, concentration-to-dose ratio; NLR, neutrophil-to-lymphocyte ratio\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6460947/v1/cf9481b92c7f241af14b9443.png"},{"id":87467396,"identity":"d31657c0-32bd-445c-8780-67229126eedd","added_by":"auto","created_at":"2025-07-24 08:09:25","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":745190,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6460947/v1/9c4b3e4e-dab0-42ab-92ee-62c57c216d21.pdf"},{"id":85746123,"identity":"94af91b6-d019-4c54-a013-be45bbf85721","added_by":"auto","created_at":"2025-07-01 09:26:24","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":23188,"visible":true,"origin":"","legend":"\u003cp\u003eSupplementary Tables 1-4\u003c/p\u003e","description":"","filename":"SupplementaryTablesR2.docx","url":"https://assets-eu.researchsquare.com/files/rs-6460947/v1/e2e7d531db0516912993ff20.docx"}],"financialInterests":"There is no conflict of interest","formattedTitle":"Elevated neutrophil-to-lymphocyte ratios correlate with increased clozapine concentration-to-dose ratios during titration","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eClozapine is a highly effective atypical antipsychotic used for the management of treatment-resistant schizophrenia; however, it is underused because of its various side effects. The ability to metabolize clozapine varies significantly among individuals.\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e Factors such as sex, smoking, and ethnicity are known to affect clozapine metabolism, and international guidelines recommend initial titration protocols that consider these factors.\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e Rapid clozapine titration that is not appropriate for an individual's metabolic capacity can lead to early inflammatory side effects such as fever, myocarditis, and pneumonia.\u003csup\u003e\u003cspan additionalcitationids=\"CR4 CR5\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e This may progress to a life-threatening condition characterized by organ damage such as myocarditis, pneumonia, nephritis, liver dysfunction, and pancreatitis, which may be accompanied by eosinophilia and rash, and is diagnosed as clozapine-associated drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome.\u003csup\u003e\u003cspan additionalcitationids=\"CR8\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e These conditions are thought to be caused by an immune hypersensitivity reaction to clozapine. The relative mortality rate of myocarditis and pneumonia associated with clozapine is significantly higher than that of clozapine-associated agranulocytosis.\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e,\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e Therefore, it is important to estimate the clozapine-metabolizing ability of an individual early in the titration phase and perform individualized titration. Measuring the clozapine concentration-to-dose (C/D) ratio helps estimate the individual metabolic capacity. Our previous study analyzing the weekly measurements of clozapine blood concentrations within 6 weeks of starting clozapine revealed that fever increased the clozapine C/D ratio.\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e Inflammation reportedly reduces the activity of cytochrome P450 (CYP) 1A2, the main enzyme involved in the metabolism of clozapine.\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e The underlying mechanism is hypothesized to be that inflammatory cytokines such as interleukin-6 and tumor necrosis factor-α suppress the transcription of CYP1A2, thereby reducing its synthesis and activity.\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e The inflammation induced by clozapine itself may impair its metabolism, leading to increased clozapine blood levels and further inflammation, creating a vicious cycle.\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e Therefore, international guidelines recommend measuring C-reactive protein (CRP) weekly for the first 4 weeks after initiating clozapine and avoiding dose increases if CRP levels rise.\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e Our previous study measured CRP levels weekly or daily during clozapine titration and reported that CRP levels were elevated in many patients even in the absence of obvious inflammatory symptoms such as fever.\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e Furthermore, we showed that the C/D ratio may temporarily increase even in patients without fever.\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e Based on these results, we hypothesized that subclinical inflammation during clozapine titration increases the clozapine C/D ratio. Most of the data on the relationship between inflammation and elevated blood clozapine levels is based on case reports, and studies with well-controlled cohorts are lacking.\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e A recent retrospective study by Smith et al. identified 126 patients who had their clozapine blood levels and CRP levels measured simultaneously, demonstrating an association between CRP and clozapine blood levels.\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e However, they were limited as the clinical context of each patient and the timing of the blood measurements (number of days after starting clozapine) were unknown, and the longitudinal change in the C/D ratio within patients was unknown.\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e Therefore, we decided to examine the relationship between inflammation and clozapine blood levels using past datasets. Although CRP was not measured simultaneously with clozapine blood levels, neutrophil and lymphocyte counts were routinely measured in clinical practice. We therefore decided to use the neutrophil/lymphocyte ratio (NLR) as a marker of inflammation.\u003c/p\u003e \u003cp\u003eNLR is a readily available, robust biomarker of inflammation, stress, and immune system activation that was proposed by Zahorec more than 20 years ago.\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e NLR is widely used in general internal medicine (inflammation and infection), intensive care medicine, oncology, surgery, and perioperative medicine, and has been established as a very sensitive marker of inflammation and stress.\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e It is also used to assess inflammation in chronic diseases, including diabetes, cancer, ischemic heart disease, and psychiatric disorders.\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e There is growing evidence suggesting that inflammation may be involved in the pathogenesis and prognosis of psychiatric disorders\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e,\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e and NLR is extensively used as an indicator of inflammation in psychiatric research.\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eThus, the present study aimed to investigate whether an increase in NLR, an alternative marker of inflammation,\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e would be associated with an increase in the C/D ratio upon reanalyzing the dataset of our previous publication,\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e in which the blood concentration of clozapine and the number of neutrophils and lymphocytes were measured simultaneously every week for 6 weeks from the start of treatment.\u003c/p\u003e"},{"header":"2 Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Study participants\u003c/h2\u003e \u003cp\u003eThe present study is a reanalysis of data from our previous publication, in which clozapine levels were measured weekly for 6 weeks after starting treatment.\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e This study is a secondary analysis of this dataset. Briefly, we retrospectively investigated the medical records of all patients at Nozoe Hills Hospital who met the following criteria: 1) patients with schizophrenia who were first treated with clozapine between April 2020 and July 2024 and 2) patients for whom clozapine blood levels were measured for at least two consecutive weeks after the start of clozapine treatment. Schizophrenia was diagnosed based on the International Classification of Diseases, 10th revision. Because this retrospective study used anonymized data, an opt-out form was displayed on the hospital\u0026rsquo;s bulletin board before data collection. Individuals who did not express their intent for exclusion were included in the study. This study was approved by the Ethics Committee of Nozoe Hills Hospital (Approval ID: 2024-6).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Measurement of clozapine blood levels\u003c/h2\u003e \u003cp\u003eAll blood concentration measurements were performed in an inpatient setting and the vital signs and medication adherence of the patients were monitored by a nurse. Smoking was prohibited at the hospital. The details of concomitant medications at the start of clozapine treatment have been described previously,\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e and there was no concomitant use of potent CYP1A2 inhibitors. Blood clozapine levels within 6 weeks of starting clozapine treatment were included in this study. Clozapine levels were measured simultaneously with weekly blood tests for white blood cell and neutrophil counts, as required in Japan, after starting clozapine. In most patients, blood was collected approximately 12 h after the last clozapine dose. Blood clozapine levels were measured by high-performance liquid chromatography at the Department of Clinical Pharmacotherapy, Hiroshima University, Hiroshima, Japan, as previously reported.\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e Blood clozapine levels measured while the temperature of the patient exceeded 38℃ until it dropped below 37℃ were classified as measurements taken during fever.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Assessment of C/D ratio and NLR\u003c/h2\u003e \u003cp\u003eThe average clozapine dose up to 5 days before the blood clozapine level measurements was used to calculate the C/D ratios for each patient. This is because the clozapine dose changed during titration, and steady-state blood concentration measurements were not available. Generally, approximately 95% of the steady-state concentration is achieved in five half-lives, and 99% is achieved in seven half-lives.\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e Assuming a half-life of 24 h for repeated doses of clozapine, a steady state can be achieved in five days.\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eThe NLR or neutrophil counts/lymphocyte counts were calculated simultaneously with the blood clozapine concentration measurement.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Statistical analysis\u003c/h2\u003e \u003cp\u003eStatistical analyses were performed using the EZR software (Jichi Medical University, Saitama, Japan). First, to roughly estimate the overall correlation, Pearson's product-moment correlation coefficient was calculated for all samples for the correlation between C/D ratio and NLR, C/D ratio and neutrophil counts, and C/D ratio and lymphocyte counts. Next, a linear mixed model with restricted maximum likelihood estimation was used to clarify the correlation between the C/D ratio and NLR in samples that were repeatedly measured within individuals. The fixed effects used to estimate the C/D ratio included the NLR (continuous variable), week (continuous variable), and the interaction between the NLR and week. We also analyzed sex, obesity (body mass index [BMI]\u0026thinsp;\u0026gt;\u0026thinsp;30), concomitant valproate use, and smoking before hospitalization as covariates in a linear mixed model as a sensitivity analysis. The random effects considered the individual variability of the intercept. Because the C/D ratio and NLR were not normally distributed, they were transformed to the natural logarithm. We performed a sensitivity analysis, excluding six patients who developed fever within 6 weeks after starting clozapine treatment. The statistical significance level was set at P\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results","content":"\u003cp\u003eA total of 28 patients were included in the study. There were 143 clozapine blood samples measured weekly within 6 weeks of clozapine initiation. Detailed patient demographics and clozapine blood concentration data are shown in Table 1. Of the 28 patients, six had fever within 6 weeks of clozapine initiation, but only three blood clozapine samples were measured during fever. In all 143 samples, the median C/D ratio (interquartile range [IQR]) was 1.43 (1.05–2.0), and the median NLR (IQR) was 1.85 (1.43–2.79). Table 2 shows ranges of C/D ratios and NLRs by week. Although we have previously reported weekly C/D ratios using the same cohort,\u003csup\u003e12\u003c/sup\u003e the present study describes a more detailed range. From weeks 1 to 3, the median NLR was significantly higher in patients with fever than in those without (Table 2). As we reported previously,\u003csup\u003e12\u003c/sup\u003e in weeks 1 and 2, the median C/D ratio was significantly higher in patients with fever than in those without (Table 2).\u003c/p\u003e\n\u003cp\u003ePearson’s product-moment correlation analysis indicated a significant correlation between the C/D ratio and neutrophil count (correlation coefficient = 0.255, 95% confidence interval [CI]: 0.0952–0.403, P \u0026lt; 0.005), as shown in Fig. 1(a). In contrast, a significant negative correlation was shown between the C/D ratio and lymphocyte count (correlation coefficient = −0.195, 95% CI: −0.348 to −0.0323, P \u0026lt; 0.05) (Fig. 1(b)). Among these analyses, the correlation between the C/D ratio and NLR was the strongest (correlation coefficient = 0.37, 95% CI: 0.22 to 0.504, P \u0026lt; 0.00001) (Fig. 1(c)).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eNext, we used a linear mixed model to examine the fixed effect of NLR on the C/D ratio in repeatedly measured samples within individuals. A significant fixed effect of NLR on C/D ratio was observed (estimate: 0.70; 95% CI: 0.47 to 0.92; P \u0026lt; 0.0001) (Table 3). Since we found significant interactions between NLR and week, we calculated an estimate of the fixed effect of NLR on the C/D ratio with the week interaction considered (Fig. 2(a)). The fixed effect of NLR was attenuated over time due to a significant negative interaction between NLR and week. (Fig. 2(a)). As a sensitivity analysis, the same analysis was performed excluding the six patients who had fever within 6 weeks after starting clozapine treatment. The results of the sensitivity analysis were generally consistent with those of the main analysis (Table 4, Fig. 2(b)). We also performed a sensitivity analysis by including sex, obesity (BMI \u0026gt; 30), concomitant use of valproic acid, and smoking before hospitalization as covariates in a linear mixed model, but no significant effect was observed for any of these factors (Supplementary Tables 1-4).\u0026nbsp;\u003c/p\u003e"},{"header":"4 Discussion","content":"\u003cp\u003eThe present study's main finding was identifying a positive correlation between NLR and C/D ratio during clozapine titration. Although the relationship between inflammation and increased blood clozapine levels has been demonstrated in numerous case reports,\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e only a few cohort studies have been conducted under well-controlled conditions.\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e In a cohort of 131 Chinese patients,\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e inflammation/infection was observed on 2% of the total monitored days (482/24,789), occurring in 18 episodes across 16 patients. Eleven percent of the infection episodes did not show any clinically relevant effect (no increase in white blood cells or CRP levels). In 61% of the infection episodes, it was recommended to reduce the clozapine dose by half, and in 28% of the infection episodes, it was recommended to reduce the clozapine dose by one-third. In a cohort of 65 hospitalized Chinese patients,\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e the clozapine C/D ratios during infection were significantly higher than at baseline, and a significant positive correlation was found between the C/D ratios and white blood cell and neutrophil counts. Recently, Smith et al. showed in a retrospective study of 126 patients that the C/D ratio was three times higher in non-smokers with high CRP levels (CRP\u0026thinsp;\u0026gt;\u0026thinsp;50 mg/L) than in those with low CRP levels (CRP\u0026thinsp;\u0026lt;\u0026thinsp;5 mg/L).\u003csup\u003e20\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eThe strength of the current study is that blood clozapine levels and NLR were measured under well-controlled conditions every week for 6 weeks after clozapine initiation during hospitalization. Furthermore, even when the six patients who had fever during clozapine titration were excluded, a significant correlation was observed between the clozapine C/D ratio and the NLR, suggesting that blood clozapine levels increased when the NLR, a marker of inflammation, was high, even when the patient was clinically asymptomatic. The reference range for NLR is 1 to 2, and values higher than 3 are considered pathological.\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e The linear mixed model of this study showed that when the NLR increased by 1%, the C/D ratio increased by 0.70%. In weeks 1 to 3, the median NLR was significantly higher in patients with fever than in those without, exceeding 3, and the median C/D ratio was also significantly higher in patients with fever than in those without in weeks 1 and 2 (Table\u0026nbsp;2). Therefore, although no clear threshold for NLR was identified in the present study, the possibility of unexpectedly high blood levels of clozapine may be considered when the NLR exceeds 3.\u003c/p\u003e \u003cp\u003eIn addition, the present study showed that the fixed effect of NLR on the C/D ratio significantly decreased over time. This fact may suggest that subclinical inflammation is likely to occur early after the start of clozapine (weeks 1\u0026ndash;3), i.e., the NLR and C/D ratio are likely to increase at this time. However, the frequency and onset time of inflammation may be affected by titration speed.\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e,\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eOur results suggest that subclinical inflammation during clozapine titration can increase blood clozapine levels more than expected and underscore the importance of CRP monitoring in detecting subclinical inflammation during clozapine titration. As international guidelines recommend measuring CRP and clozapine blood levels weekly after starting clozapine,\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e clinicians should monitor CRP and clozapine blood levels.\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e CRP levels were markedly higher than the reference range in all samples during fever (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e; n\u0026thinsp;=\u0026thinsp;5). Considering that the median NLR was significantly higher in patients with fever than in those without (Table\u0026nbsp;2), CRP, NLR, and C/D ratio may be correlated. However, although CRP and NLR are both inflammatory biomarkers, there may be differences in the timing and degree of elevation between CRP and NLR, and further studies are needed regarding their clinical applicability.\u003c/p\u003e \u003cp\u003eThe results of this study show that clinicians can estimate inflammation and elevated clozapine blood levels using neutrophil and lymphocyte counts, which are routinely measured in clinical practice during clozapine titration. By monitoring CRP levels and NLR during clozapine titration, clinicians can detect subclinical inflammation early and take measures such as temporarily halting titration, thereby preventing the progression of clozapine-induced life-threatening conditions such as myocarditis, pneumonia, and DRESS syndrome.\u003c/p\u003e \u003cp\u003eIn this cohort, the median clozapine dose at week 4 was 75 mg/day, and the median clozapine blood level at week 4 was 116 ng/mL. In a study of 1,408 Korean inpatients, the average clozapine dose was approximately 200 mg/day after 4\u0026ndash;8 weeks of initiation, and the average C/D ratio was 1.23 ng/mL per mg/day.\u003csup\u003e34\u003c/sup\u003e International guidelines recommend the slowest titration for non-smoking Asian women, with 175 mg/day for normal metabolizers and 75 mg/day for poor metabolizers at week 4 after starting clozapine.\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e Naturalistic observations may indicate that Asian populations tolerate clozapine at lower doses than European populations.\u003c/p\u003e \u003cp\u003eThis study has several limitations. First, the number of patients included was small. Further studies with larger sample sizes are needed to confirm our results. Second, it is difficult to use steady-state concentrations during titration; therefore, the average dose over the five days before measuring blood concentration was used to calculate the C/D ratio. However, since the participants in the present study were titrated very slowly (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e),\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e the clozapine dose remained almost unchanged over 5 days, and this limitation had little effect on our findings. Finally, this study was conducted entirely on Japanese patients; therefore, while it has the advantage of being a homogeneous ethnic group, it cannot be generalized to other populations. Japanese people belong to the East Asian ethnic group and have the lowest clozapine metabolism capacity among all ethnic groups.\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e International guidelines recommend the slowest titration speed for Japanese people.\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e The frequency of inflammatory side effects caused by clozapine is reported to be higher in Japanese people than in Europeans.\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e It cannot be ruled out that both clozapine metabolism capacity and immunological responsiveness to clozapine differ among ethnic groups. Therefore, future studies should clarify the relationship between clozapine titration and inflammation in other ethnic groups.\u003c/p\u003e \u003cp\u003eIn conclusion, this study suggests a positive correlation between the C/D ratio and NLR during clozapine titration. Our findings indicate that subclinical inflammation in the early titration phase affects the pharmacokinetics of clozapine.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eData availability statement\u003c/p\u003e\n\u003cp\u003eThe data are not publicly available because they contain information that could compromise the research participants\u0026rsquo; privacy/consent.\u003c/p\u003e\n\u003cp\u003eAcknowledgements\u003c/p\u003e\n\u003cp\u003eWe would like to thank Editage (www.editage.jp) for\u0026nbsp;the English language editing.\u003c/p\u003e\n\u003cp\u003eFunding\u003c/p\u003e\n\u003cp\u003eThis research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.\u003c/p\u003e\n\u003cp\u003eCompeting\u0026nbsp;Interests\u003c/p\u003e\n\u003cp\u003eThe authors declare that this study was conducted in the absence of any commercial or financial relationships that could be construed as potential conflicts of interest.\u003c/p\u003e\n\u003cp\u003eAuthor Contributions\u003c/p\u003e\n\u003cp\u003eBunichiro Onodera: Formal analysis, Writing - original draft. Mutsumi Sakata: Investigation, Writing - review \u0026amp; editing. Kazuro Ikawa: Investigation, Writing - review \u0026amp; editing. Daisuke Kume: Investigation, Writing - review \u0026amp; editing. Naoki Horikawa: Investigation, Writing - review \u0026amp; editing. Hiroshi Komatsu: Supervision, Writing - review \u0026amp; editing. Takuhiro Yamaguchi: Methodology, Formal analysis, Writing - Review \u0026amp; Editing. Hiroaki Tomita: Supervision, Writing - review \u0026amp; editing. Yuki Kikuchi: Conceptualization, Formal analysis, Methodology, Project administration, Writing - review \u0026amp; editing.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003ede Leon, J. et al. 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A rational use of clozapine based on adverse drug reactions, pharmacokinetics, and clinical pharmacopsychology. \u003cem\u003ePsychother Psychosom\u0026nbsp;\u003c/em\u003e\u003cstrong\u003e89\u003c/strong\u003e, 200\u0026ndash;214 (2020).\u003c/li\u003e\n \u003cli\u003eRuan, C.-J., Zang, Y.-N., Cheng, Y.-H., Wang, C.-Y. \u0026amp; de Leon, J.\u0026nbsp;Around 3% of 1,300 levels were elevated during infections in a retrospective review of 131 Beijing hospital in-patients with more than 24,000 days of clozapine treatment. \u003cem\u003ePsychother Psychosom\u003c/em\u003e\u003cstrong\u003e89\u003c/strong\u003e, 255-257 (2020).\u003c/li\u003e\n \u003cli\u003eZahorec, R. Neutrophil-to-lymphocyte ratio, past, present and future perspectives. \u003cem\u003eBratisl Lek Listy\u0026nbsp;\u003c/em\u003e\u003cstrong\u003e122\u003c/strong\u003e, 474-488 (2021).\u003c/li\u003e\n \u003cli\u003eKikuchi, Y. et al. Slower clozapine titration is associated with delayed onset of clozapine-induced fever among Japanese patients with schizophrenia. \u003cem\u003eSchizophr\u003c/em\u003e\u003cstrong\u003e9\u003c/strong\u003e, 82 (2023).\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eKikuchi, Y. et al. Relationship between clozapine-induced inflammation and eosinophilia: a retrospective cohort study. \u003cem\u003eSchizophr Bull.\u003c/em\u003e Preprint at doi.org/10.1093/schbul/sbae213 (2024).\u003c/li\u003e\n \u003cli\u003eLeung, J. G. et al. A systematic review of clozapine-associated inflammation and related monitoring. \u003cem\u003ePharmacotherapy\u003c/em\u003e\u003cstrong\u003e43\u003c/strong\u003e, 1364\u0026ndash;1396 (2023).\u003c/li\u003e\n \u003cli\u003eKang, N. et al. Association between initial pattern of clozapine titration, concentration-to-dose ratio, and incidence of fever in patients with schizophrenia spectrum disorders in a Korean tertiary hospital. \u003cem\u003eSchizophr Res\u003c/em\u003e\u003cstrong\u003e268\u003c/strong\u003e, 131\u0026ndash;137 (2024).\u003c/li\u003e\n \u003cli\u003eSchoretsanitis, G., \u0026amp; de Leon, J. Best practices for starting clozapine in patients with schizophrenia: how to switch from the prior antipsychotic(s). \u003cem\u003eJ Clin Psychiatry\u003c/em\u003e\u003cstrong\u003e83\u003c/strong\u003e, 22ac14500 (2022). \u0026nbsp;\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 738px;\"\u003e\n \u003cp\u003eTable 1: Patient characteristics and blood clozapine measurements\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 501px;\"\u003e\n \u003cp\u003eNumber of patients\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 238px;\"\u003e\n \u003cp\u003e28\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 501px;\"\u003e\n \u003cp\u003eFemale, n (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 238px;\"\u003e\n \u003cp\u003e15 (54)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 501px;\"\u003e\n \u003cp\u003eAge, year, mean (SD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 238px;\"\u003e\n \u003cp\u003e30.6 (16.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 501px;\"\u003e\n \u003cp\u003eBMI, kg/m\u003csup\u003e2\u003c/sup\u003e, mean (SD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 238px;\"\u003e\n \u003cp\u003e23.3 (5.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 501px;\"\u003e\n \u003cp\u003eObesity (BMI\u0026gt;30), n (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 238px;\"\u003e\n \u003cp\u003e3 (11)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 501px;\"\u003e\n \u003cp\u003eSmoking before starting clozapine, n (%)\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 238px;\"\u003e\n \u003cp\u003e4 (14)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 501px;\"\u003e\n \u003cp\u003eConcomitant valproate at clozapine initiation, n (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 238px;\"\u003e\n \u003cp\u003e8 (29)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 501px;\"\u003e\n \u003cp\u003eBody temperature before starting clozapine, ℃, median (min, IQR, max)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 238px;\"\u003e\n \u003cp\u003e36.4 (35.3, 36.2\u0026ndash;36.6, 37.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 501px;\"\u003e\n \u003cp\u003ePatient with fever, n (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 238px;\"\u003e\n \u003cp\u003e6 (21)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 501px;\"\u003e\n \u003cp\u003eNumber of clozapine blood levels measured, n\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 238px;\"\u003e\n \u003cp\u003e143\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 501px;\"\u003e\n \u003cp\u003eNumber of measurements during fever, n (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 238px;\"\u003e\n \u003cp\u003e3 (2.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 501px;\"\u003e\n \u003cp\u003eCRP levels measured during fever, mg/dL, mean (SD) (n = 5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 238px;\"\u003e\n \u003cp\u003e8.61 (4.85)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 501px;\"\u003e\n \u003cp\u003eClozapine dose, mg/day, median (min,\u0026nbsp;IQR, max)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 238px;\"\u003e\n \u003cp\u003e75 (25,\u0026nbsp;45\u0026ndash;100, 300)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 501px;\"\u003e\n \u003cp\u003eClozapine blood levels, ng/mL, median (min,\u0026nbsp;IQR, max)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 238px;\"\u003e\n \u003cp\u003e93 (13,\u0026nbsp;57\u0026ndash;153.5, 626)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 501px;\"\u003e\n \u003cp\u003eC/D ratio, (ng/mL)/(mg/day), median (min,\u0026nbsp;IQR, max)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 238px;\"\u003e\n \u003cp\u003e1.43 (0.26,\u0026nbsp;1.05\u0026ndash;2.0, 6.96)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 501px;\"\u003e\n \u003cp\u003eWhite blood cell count, \u0026times;10\u003csup\u003e3\u003c/sup\u003e/mm\u003csup\u003e3\u003c/sup\u003e, median (min,\u0026nbsp;IQR, max)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 238px;\"\u003e\n \u003cp\u003e6.02 (4.0,\u0026nbsp;5.20\u0026ndash;7.68, 17.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 501px;\"\u003e\n \u003cp\u003eNeutrophil count, \u0026times;10\u003csup\u003e3\u003c/sup\u003e/mm\u003csup\u003e3\u003c/sup\u003e, median, (min,\u0026nbsp;IQR, max)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 238px;\"\u003e\n \u003cp\u003e3.42 (2.01,\u0026nbsp;2.61\u0026ndash;4.65, 12.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 501px;\"\u003e\n \u003cp\u003eLymphocyte count, \u0026times;10\u003csup\u003e3\u003c/sup\u003e/mm\u003csup\u003e3\u003c/sup\u003e, median (min,\u0026nbsp;IQR, max)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 238px;\"\u003e\n \u003cp\u003e1.91 (0.42,\u0026nbsp;1.43\u0026ndash;2.33, 4.61)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 501px;\"\u003e\n \u003cp\u003eNLR, median (min,\u0026nbsp;IQR, max)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 238px;\"\u003e\n \u003cp\u003e1.85 (0.75,\u0026nbsp;1.42\u0026ndash;2.79, 9.14)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 738px;\"\u003e\n \u003cp\u003e1: Smoking was prohibited during clozapine titration.\u003c/p\u003e\n \u003cp\u003eBMI, body mass index; C/D, concentration-to-dose; CRP, C-reactive protein;\u0026nbsp;IQR, interquartile range; NLR, neutrophil-to-lymphocyte ratio; min, minimum; max; maximum\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\" style=\"width: 95px;\"\u003e\n \u003cp\u003eTable 2: Ranges of weekly C/D ratios and NLRs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 4px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 11px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 39px;\"\u003e\n \u003cp\u003eC/D ratio, median (min, IQR, max)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 4px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 1px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 39px;\"\u003e\n \u003cp\u003eNLR, median (min, IQR, max)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 4px;\"\u003e\n \u003cp\u003e \u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 11px;\"\u003e\n \u003cp\u003e \u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003ePatients with fever\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003ePatients without fever\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 4px;\"\u003e\n \u003cp\u003eP\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 1px;\"\u003e\n \u003cp\u003e \u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003ePatients with fever\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003ePatients without fever\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 4px;\"\u003e\n \u003cp\u003eP\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 11px;\"\u003e\n \u003cp\u003eWeek 1 (n =28)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e2.12 (1.43, 1.87\u0026ndash;3.06, 4.49)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e1.31 (0.35, 0.94\u0026ndash;1.88, 2.80)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 4px;\"\u003e\n \u003cp\u003e0.022\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 1px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e3.16 (1.46, 2.32\u0026ndash;4.53, 9.14)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e1.31 (0.79, 1.14\u0026ndash;1.56, 2.98)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 4px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 11px;\"\u003e\n \u003cp\u003eWeek 2 (n =28)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e3.48 (1.68, 2.30\u0026ndash;4.18, 6.96)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e1.23 (0.35, 0.94\u0026ndash;2.12, 2.82)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 4px;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 1px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e3.50 (2.04, 3.36\u0026ndash;4.50, 7.36)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e1.76 (0.75, 1.48\u0026ndash;2.33, 5.34)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 4px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 11px;\"\u003e\n \u003cp\u003eWeek 3 (n =25)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e2.80 (1.20, 1.60\u0026ndash;4.20, 5.20)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e1.32 (0.55, 1.14\u0026ndash;1.67, 4.10)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 4px;\"\u003e\n \u003cp\u003e0.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 1px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e4.57 (2.95, 3.74\u0026ndash;4.57, 6.49)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e1.86 (0.93, 1.21\u0026ndash;2.22, 7.96)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 4px;\"\u003e\n \u003cp\u003e0.0085\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 11px;\"\u003e\n \u003cp\u003eWeek 4 (n =27)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e1.12 (0.94, 1.07\u0026ndash;1.83, 2.59)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e1.33 (0.26, 1.03\u0026ndash;1.73, 3.42)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 4px;\"\u003e\n \u003cp\u003e0.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 1px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e3.17 (1.61, 3.14\u0026ndash;5.86, 5.88)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e1.89 (0.95, 1.45\u0026ndash;2.45, 7.89)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 4px;\"\u003e\n \u003cp\u003e0.055\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 11px;\"\u003e\n \u003cp\u003eWeek 5 (n =18)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e2.01 (1.12, 1.75\u0026ndash;2.10, 2.27)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e1.33 (0.43, 1.18\u0026ndash;2.07, 2.76)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 4px;\"\u003e\n \u003cp\u003e0.57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 1px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e2.28 (1.61, 1.69\u0026ndash;3.47, 5.38)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e1.97 (0.94, 1.48\u0026ndash;2.47, 4.95)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 4px;\"\u003e\n \u003cp\u003e0.442\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 11px;\"\u003e\n \u003cp\u003eWeek 6 (n =17)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e1.49 (1.26, 1.38\u0026ndash;2.12, 2.74)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e1.32 (0.28, 1.02\u0026ndash;1.59, 2.64)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 4px;\"\u003e\n \u003cp\u003e0.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 1px;\"\u003e\n \u003cp\u003e \u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e1.87 (1.49, 1.68\u0026ndash;3.44, 5.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e1.61 (0.85, 1.20\u0026ndash;3.31, 7.49)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 4px;\"\u003e\n \u003cp\u003e0.59\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"8\" style=\"width: 100px;\"\u003e\n \u003cp\u003e1: The weekly C/D ratios and NLRs were compared between patients with and without fever using the Mann\u0026ndash;Whitney U test.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"8\" style=\"width: 100px;\"\u003e\n \u003cp\u003eC/D, concentration-to-dose; IQR, interquartile range; NLR, neutrophil-to-lymphocyte ratio; min, minimum; max; maximum\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"735\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"6\" style=\"width: 631px;\"\u003e\n \u003cp\u003eTable 3: Estimates of fixed effects on the C/D ratio in a linear mixed model (all patients)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 153px;\"\u003e\n \u003cp\u003e \u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 97px;\"\u003e\n \u003cp\u003e \u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e \u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 236px;\"\u003e\n \u003cp\u003e95% confidence interval\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003e \u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e \u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 153px;\"\u003e\n \u003cp\u003e \u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 97px;\"\u003e\n \u003cp\u003eEstimate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003eSE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 118px;\"\u003e\n \u003cp\u003eLower limit\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 118px;\"\u003e\n \u003cp\u003eUpper limit\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003eT value\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003eP\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 153px;\"\u003e\n \u003cp\u003eNLR\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 97px;\"\u003e\n \u003cp\u003e0.70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 118px;\"\u003e\n \u003cp\u003e0.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 118px;\"\u003e\n \u003cp\u003e0.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003e6.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e\u0026lt; 0.0001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 153px;\"\u003e\n \u003cp\u003eWeek\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 97px;\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 118px;\"\u003e\n \u003cp\u003e\u0026minus;0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 118px;\"\u003e\n \u003cp\u003e0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003e0.69\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e0.493\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 153px;\"\u003e\n \u003cp\u003eNLR \u0026times;\u0026nbsp;Week\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 97px;\"\u003e\n \u003cp\u003e\u0026minus;0.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 118px;\"\u003e\n \u003cp\u003e\u0026minus;0.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 118px;\"\u003e\n \u003cp\u003e\u0026minus;0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003e\u0026minus;3.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e\u0026lt; 0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\" style=\"width: 735px;\"\u003e\n \u003cp\u003eNote: Number of patients = 28; Number of blood samples = 143\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\" style=\"width: 735px;\"\u003e\n \u003cp\u003eThe C/D ratio and NLR were converted to natural logarithms.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\" style=\"width: 735px;\"\u003e\n \u003cp\u003eC/D, concentration-to-dose; NLR, neutrophil-to-lymphocyte ratio; SE, standard error\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"735\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\" valign=\"top\" style=\"width: 735px;\"\u003e\n \u003cp\u003eTable 4: Estimates of fixed effects on the C/D ratio in a linear mixed model (excluding the six patients with fever)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 189px;\"\u003e\n \u003cp\u003e \u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 120px;\"\u003e\n \u003cp\u003e \u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003e \u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 208px;\"\u003e\n \u003cp\u003e95% CI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e \u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e \u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 189px;\"\u003e\n \u003cp\u003e \u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 120px;\"\u003e\n \u003cp\u003eEstimate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003eSE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003eLower limit\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003eUpper limit\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003eT value\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003eP\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 189px;\"\u003e\n \u003cp\u003eNLR\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 120px;\"\u003e\n \u003cp\u003e0.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003e0.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e0.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e0.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e3.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e\u0026lt; 0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 189px;\"\u003e\n \u003cp\u003eWeek\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 120px;\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e\u0026minus;0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e0.84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e0.40\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 189px;\"\u003e\n \u003cp\u003eNLR \u0026times;\u0026nbsp;Week\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 120px;\"\u003e\n \u003cp\u003e\u0026minus;0.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e\u0026minus;0.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e\u0026minus;0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e\u0026minus;2.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e0.024\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\" style=\"width: 735px;\"\u003e\n \u003cp\u003eNote: Number of patients = 22; Number of blood samples = 115\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\" style=\"width: 735px;\"\u003e\n \u003cp\u003eThe C/D ratio and NLR were converted to natural logarithms.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\" style=\"width: 735px;\"\u003e\n \u003cp\u003eC/D, concentration-to-dose; NLR, neutrophil-to-lymphocyte ratio; SE, standard error\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":true,"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":"C-reactive protein, drug monitoring, fever, inflammation, precision medicine","lastPublishedDoi":"10.21203/rs.3.rs-6460947/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6460947/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eFew cohort studies have examined the relationship between inflammation and increased clozapine blood levels. The purpose of this study was to investigate the relationship between the neutrophil-to-lymphocyte ratio (NLR), a marker of inflammation, and the clozapine concentration-to-dose (C/D) ratio during clozapine titration. We retrospectively investigated the medical records of all patients at Nozoe Hills Hospital who met the following criteria: 1) patients with schizophrenia who were first treated with clozapine between April 2020 and July 2024 and 2) patients for whom clozapine blood levels were measured for at least two consecutive weeks after the start of clozapine treatment. The study included 143 blood samples from 28 patients collected within 6 weeks of starting clozapine treatment. A linear mixed model with random intercepts was used to determine the correlation between the clozapine C/D ratio and NLR in samples repeatedly measured within an individual. Fixed effects for the C/D ratio included NLR, week, and the interaction between NLR and week. A significant fixed effect of NLR on C/D ratio was observed (estimate: 0.70; 95% confidence interval: 0.47–0.92; P\u0026lt;0.0001). The fixed effect of NLR was attenuated over time due to a significant negative interaction between NLR and week. The fixed effect of NLR remained significant even after excluding the six patients who had fever during clozapine titration. This study suggests a positive correlation between the C/D ratio and NLR during clozapine titration. Our findings indicate that subclinical inflammation in the early titration phase affects the pharmacokinetics of clozapine.\u003c/p\u003e","manuscriptTitle":"Elevated neutrophil-to-lymphocyte ratios correlate with increased clozapine concentration-to-dose ratios during titration","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-01 09:18:20","doi":"10.21203/rs.3.rs-6460947/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":"58a900d7-b0ff-40e6-acd5-9416afafd61c","owner":[],"postedDate":"July 1st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":50385352,"name":"Health sciences/Biomarkers"},{"id":50385353,"name":"Biological sciences/Drug discovery/Pharmacology"}],"tags":[],"updatedAt":"2025-07-24T07:35:16+00:00","versionOfRecord":{"articleIdentity":"rs-6460947","link":"https://doi.org/10.1038/s41537-025-00648-4","journal":{"identity":"schizophrenia","isVorOnly":true,"title":"Schizophrenia"},"publishedOn":"2025-07-10 04:00:00","publishedOnDateReadable":"July 10th, 2025"},"versionCreatedAt":"2025-07-01 09:18:20","video":"","vorDoi":"10.1038/s41537-025-00648-4","vorDoiUrl":"https://doi.org/10.1038/s41537-025-00648-4","workflowStages":[]},"version":"v1","identity":"rs-6460947","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6460947","identity":"rs-6460947","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}