Evaluation of Ravulizumab Trough Levels in Pediatric Atypical Hemolytic Uremic Syndrome in Remission

Evaluation of Ravulizumab Trough Levels in Pediatric Atypical Hemolytic Uremic Syndrome in Remission | 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 Research Article Evaluation of Ravulizumab Trough Levels in Pediatric Atypical Hemolytic Uremic Syndrome in Remission Samara M Mendez Nunez, Samantha A Brokenshire, Poyyapakkam Srivaths, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7216678/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 10 Jan, 2026 Read the published version in Pediatric Nephrology → Version 1 posted 5 You are reading this latest preprint version Abstract Background Ravulizumab drug monitoring has not been explored for maintenance therapy in patients with atypical hemolytic uremic syndrome (aHUS). Phase III trials suggest standard dosing regimen provides troughs about 3-fold higher than needed to suppress complement activity. We describe the use of ravulizumab in pediatric patients with aHUS in remission, exploring potential modified dosing strategies based on serum drug level and complement markers. Methods This single-center, retrospective cohort study included pediatric patients with aHUS in remission receiving outpatient ravulizumab infusions between June 30, 2023 and March 31, 2024 with at least one ravulizumab trough. Patients received a standard (SR) or a modified (MR) regimen, determined by the nephrologist. The primary outcome was to describe troughs and corresponding AH50 for patients on at least two equal doses. Secondary outcomes included comparison of troughs by regimen, intra-patient variability, possible adverse drug events (pADE), and drug costs. Results Nine patients were included. The mean ravulizumab trough level was 399.1 (± 107.3) mcg/mL. All patients exceeded goal of 175 mcg/mL and achieved AH50 < 10%. Four patients (44%) received ravulizumab according to a MR. No difference was observed in ravulizumab trough levels between SR and MR groups (p = 0.67). Patients with multiple troughs showed low intra-patient variability (CV < 25%). pADE rates were similar across regimens, and MR was associated with lower drug costs. Conclusion Individualized maintenance regimens of ravulizumab based on trough and complement monitoring appears safe and effective while reducing drug costs. Further study is needed to define optimal ravulizumab maintenance dosing strategy. Ravulizumab Complement inhibitor Pediatrics Atypical Hemolytic Uremic Syndrome Pharmacokinetics Figures Figure 1 Figure 2 INTRODUCTION Ravulizumab is a long-acting complement inhibitor indicated for the treatment of atypical hemolytic uremic syndrome (aHUS), a rare variant of thrombotic microangiopathy associated with uncontrolled activation of the alternative complement pathway [ 1 – 3 ]. Ravulizumab binds to complement protein C5, thereby preventing the generation of the terminal complex C5b-9 (Membrane Attack Complex, MAC) and subsequent complement-mediated endothelial damage [ 1 , 4 – 5 ]. Ravulizumab was derived from modifications to the backbone of eculizumab which reduces endosomal degradation, increases elimination half-life by four-fold and extends dosing interval to every 4–8 weeks based on a FDA-approved, weight-based dosing scheme [ 5 – 10 ]. Individualized anti-complement dosing regimens based on therapeutic drug monitoring (TDM), markers of complement activity, or a combination of both have been suggested in response to high medication costs, frequent infusions visits, and serious safety concerns for long-term complement suppression [ 11 ]. Published reports in aHUS have been limited to pharmacokinetic models or a small number of patients receiving eculizumab [ 12 – 18 ]. Only one pharmacokinetic–pharmacodynamic simulation model has been published for ravulizumab and was designed to reflect patients with paroxysmal nocturnal hemoglobinuria [ 19 ]. No real-world studies have been reported in pediatrics. Rationale for these modified dosing strategies for eculizumab and ravulizumab stems from a robust exposure-response relationship and mean trough concentrations which exceed previously established efficacy thresholds [ 9 , 16 , 20 – 22 ]. Alexion Pharmaceuticals, Inc reports that ravulizumab trough concentrations > 175 mcg/mL result in complete complement blockade, defined as free C5 < 0.5 mcg/mL [ 9 ]. However, the observed mean (coefficient of variation, %CV) ravulizumab serum trough concentration at the approved dose in the maintenance phase in phase III clinical trials were 507 (42.5), 683 (46.1), and 549 (34.1) mcg/mL for adult (N = 46), children < 20 kg (N = 7) and children ≥ 20 to < 40 kg (N = 6), respectively [ 6 – 9 ]. This exposure is nearly three-times higher than the recommended therapeutic threshold, suggesting patients could be at increased risk for dose-dependent adverse events and may be able to maintain adequate drug coverage with lower doses. However, the small number of pediatric patients included in the phase III clinical trial (N = 10) limits one’s ability to extrapolate these results to a larger population [ 8 ]. Additionally, the free C5 assay used in these trials is not readily available clinically to confirm adequate complement blockade in patients with aHUS treated with complement inhibitors [ 16 , 20 ]. Functional assays, including AH50 and CH50, which are commonly used in clinical practice were not included in major studies on ravulizumab for aHUS [ 5 – 9 ]. This study serves to describe ravulizumab trough levels and corresponding AH50 in a pediatric cohort of aHUS in remission, exploring (1) the difference of ravulizumab trough levels for patients receiving standard regimen (SR) compared to TDM-guided, modified regimen (MR), (2) the intra-individual variability in serum trough levels on stable ravulizumab dose, (3) the percentage of patients with incomplete complement suppression, defined as AH50 ≥ 10% (4) the rates of possible adverse drug events (pADE) for patients with higher serum trough levels, and (5) the trend of serum trough and AH50 levels after discontinuing therapy. METHODS Study Design and Setting We performed a single-center, retrospective cohort study of pediatric patients with documented aHUS receiving outpatient ravulizumab infusions between June 30, 2023 and March 31, 2024. Study procedures were limited to medical record review. Institutional Review Board approval was obtained from Baylor College of Medicine (Protocol H-54545). A waiver of consent was approved given the retrospective nature of the study with minimal risk to patients. Reporting of this study is in accordance with the Strengthening the Reporting of Observational studies in Epidemiology (STROBE) statement and Declaration of Helsinki. Participants and Study Size Eligible patients were < 18 years old and had a documented diagnosis of complement-mediated atypical aHUS, received at least two equal maintenance doses of ravulizumab before the end of study period, and had at least one ravulizumab trough level and one AH50 activity level recorded since ravulizumab initiation. AH50 was selected as the preferred functional assay for complement activity as it has been shown to consistently reflect decreased complement activity with increasing concentrations of ravulizumab and align with clinical trials in expected exposure-response relationship [ 22 ]. Patients who had documented laboratory signs consistent with active aHUS (platelet count 1.5x upper normal limit) since June 30, 2023 were excluded. Data Sources Data on patient demographic characteristics, past medical history, medication history, laboratory tests, and vital signs were obtained from electronic medical record (EMR) at the end of the study period. Selected laboratory results, including ravulizumab trough levels and AH50 activity levels, were obtained through laboratory services from Mayo Clinic Laboratories. AH50 assays are performed by ELISA through the measurement of the proprietary detection antibody targeting MAC [ 24 ]. Any pADE was obtained through review of clinical notes from in-person and telephonic consultations, infusion visits, or hospital admissions and the clinical problem list documented in the EMR. Exposures and Outcomes All patients received maintenance ravulizumab infusions at the discretion of their primary nephrologist. Ravulizumab exposure was evaluated using the serum trough level drawn after at least two equal maintenance doses. At the time of each trough level, the patient’s ravulizumab dosing regimen was classified as SR or MR. SR was defined as ravulizumab dose and dosing interval that matched the package insert for the patient’s weight at that time. MR was selected if their dose or dosing interval differed from the package insert. Rationale for selecting a MR was also collected if described in the EMR. The primary objective was to describe troughs and corresponding AH50 for pediatric patients with aHUS on a stable ravulizumab regimen. For the purposes of this study, adequate complement suppression was defined as AH50 < 10% [ 24 ]. If a patient had ravulizumab discontinued during the study period, all ravulizumab levels and AH50 were collected until the end of the study period. Additional laboratory markers, including CH50, SC5b9, LDH, haptoglobin, and urine protein-to-creatinine ratio (UPC), were collected as available (Online Resource 1) but not included in primary analyses. This study sought to determine if higher ravulizumab exposure was associated with higher rates of pADE. Side effects evaluated included documented new or worsening headaches, diarrhea, fatigue, alopecia, dizziness, infusion site reactions, increased transaminases, hypertensive urgency, and infections requiring antibiotics or hospital admission. These pADE were selected after reviewing common or serious adverse reactions reported in the package insert or case reports [ 5 ]. When appropriate, side effects were defined using the Common Terminology Criteria for Adverse Events (CTCAE) version 5.0. Hypertensive urgency was defined as a blood pressure (BP) of ≥ 30 mmHg above the 95th percentile in children or a BP > 180/120 mmHg in adolescents requiring intermittent anti-hypertensive medications for BP control [ 25 ]. Statistical Analyses Continuous variables were presented as means with standard deviations and categorical variables as frequencies with percentages. Normal distribution was assessed using the Shapiro-Wilk test. Nested t-test was used to compare the mean ravulizumab trough levels between dosing regimens. The assessment of the intra-patient variability of ravulizumab trough levels was done descriptively and through the paired t-test, using the first two trough levels for patients with multiple levels collected on the same dosing regimen. Pearson correlation was used to test the relationship between ravulizumab drug levels and AH50. The comparison of the incidence of pADE was performed using the Fisher’s Exact test. A post-hoc power analysis was not conducted. RESULTS Patient Selection and Descriptive Data Twelve patients receiving outpatient ravulizumab were screened for eligibility. Nine patients, of which 27 drug levels resulted, were included. All excluded patients were receiving ravulizumab for an alternative indication (n = 2 with C3 glomerulopathy, n = 1 with paroxysmal nocturnal hemoglobinuria). Baseline characteristics and ravulizumab dosing regimens are reported in Table 1 . Seven patients had complement gene mutations identified (n = 2 with CFH mutation, n = 2 with C3 gene mutation, n = 1 with CFHR1 homozygous deletion, n = 1 with CFI variant of unknown significance, and n = 1 with Factor H autoantibody associated with CFHR3/CFHR1 and CFHR1/CFHR4 deletion). Ravulizumab was continued for Patient 2 due to elevated Factor H autoantibodies (mean 90.1 units/mL [SD 16.9] during study period, normal < 22 units/mL). The median age and weight at the start of ravulizumab use was 4.3 years (IQR 2.2–13.4) and 17.8 kg (IQR 12-39.3), respectively. At the time the first trough was measured, the median weight was 19.1 kg (IQR 14.6–50.8). Five patients were receiving maintenance ravulizumab dosing defined as SR (Patients 1–5). The other four patients were receiving a MR (Patients 6–9), where dose was not increased for weight gain (n = 4) and dosing interval was extended due to scheduling conflicts (n = 1). Other documented rationale for MR included elevated troughs (n = 4), clinical stability (n = 4), and concern for pADE (n = 1). No patients were receiving kidney replacement therapy at the initiation of ravulizumab or during the study period. Proteinuria, assessed using UPC, was included as a surrogate marker to explain potential urinary ravulizumab losses [ 26 – 27 ]. Seven of the patients had proteinuria, defined as median UPC ≥ 0.2 mg/mg, during the study period (Online Resource 1). Two patients had severe proteinuria, defined as median UPC > 2 mg/mg (Patient 5, UPC 7.1 [IQR 5.7–11.3] and Patient 7, UPC 3 mg/mg [IQR 2.2–4.3]). Both patients had Stage III acute kidney injury, requiring prolonged dialysis, at initial aHUS presentation. Kidney biopsies completed after systemic signs of aHUS had resolved showed chronic changes and scarring. All patients within the cohort had normal serum albumin and none were suspected to have isolated renal thrombotic microangiopathy. Table 1 Baseline patient characteristics at the time of the first ravulizumab trough level measurement collection. (C3, complement component 3; CFH, complement factor H; CFHR1, complement factor H related 1, CFHR3, complement factor H related 3; CFHR4, complement factor H related 4; CFI, complement factor I; F, female; M, male; MR, maintenance regimen; SR, standard regimen) ID Sex Complement Gene Mutation Age (years) Weight (kg) Ravulizumab Regimen Time on current regimen (years) Total time on ravulizumab (years) Dosing Regimen 1 F CFH CFHR3/CFHR1 , homozygous deletion 4.5 15.6 600 mg every 4 weeks 2.2 2.2 SR 2 F CFHR3/CFHR1 deletion CFHR1/CFHR4 deletion FHAA 17.5 55.2 3000 mg every 8 weeks 4.0 4.0 SR 3 M CFHR1 homozygous deletion 6.1 19.1 600 mg every 4 weeks 1.8 1.9 SR 4 F None 17 60.1 3300 mg every 8 weeks 0.5 0.5 SR 5 F CFI variant of unknown significance 2.9 14.6 600 mg every 4 weeks 0.4 0.5 SR 6 M C3 CFHR3/CFHR1 , heterozygous deletion 16.3 50.8 2700 mg every 8 weeks 1.6 1.6 MR 7 F CFH 1 11.2 300 mg every 4 weeks 0.2 0.4 MR 8 M None 2.2 10.1 300 mg every 4 weeks 0.1 0.9 MR 9 F C3 CFHR3/CFHR1 , homozygous deletion 10.9 41.9 2700 mg every 10 weeks 1.5 1.6 MR Ravulizumab Pharmacokinetics and Functional Assays Ravulizumab trough levels drawn while patients were receiving stable maintenance regimens (n = 20) and corresponding laboratory measures are shown in Table 2 . The mean ravulizumab trough level of the entire cohort was 399.1 ± 107.3 mcg/mL, with all the levels above the goal of 175 mcg/mL. The mean ravulizumab trough levels for patients on SR and MR were 363.7 ± 114.1 mcg/mL and 434.6 ± 92.1 mcg/mL, respectively (Fig. 1 ). Both patients with severe proteinuria had mean trough levels above the cohort’s mean. No statistical difference was observed in the trough levels between groups (p = 0.67). The mean coefficient of variation in the six patients with multiple levels collected was reported below 25% (7.8 ± 7.4%). Additionally, a non-significant statistical difference was observed between the first and second trough levels collected in those six patients (p = 0.89). Table 2 Ravulizumab trough levels and AH50 levels description. Results for trough levels are mean ± SD. Detection limit of AH50 activity level test is < 10% (CV, coefficient of variation; MR, maintenance regimen; SD, standard deviation; SR, standard regimen) Number of troughs Ravulizumab trough level (mcg/mL) Range (mcg/mL) CV (%) AH50 (%) Total (N = 9) 20 399.1 (107.3) 232.5–558 26.9 < 10 SR (n = 5) 10 363.7 (114.1) 232.5–558 31.4 < 10 Patient 1 4 263.5 (29.9) 232.5–286 11.3 < 10 Patient 2 2 541.5 (23.3) 525–558 4.3 < 10 Patient 3 1 289 (0) - - < 10 Patient 4 1 412 (0) - - < 10 Patient 5 2 399.3 (10.3) 389-409.5 3.6 < 10 MR (n = 4) 10 434.6 (92.1) 304.3-545.9 21.2 < 10 Patient 6 4 208 (27.7) 484.3-545.9 5.4 < 10 Patient 7 3 437.9 (92.9) 347-532.7 21.2 < 10 Patient 8 1 388 (0) - - < 10 Patient 9 2 306.2 (2.6) 304.3–308 0.9 < 10 Ravulizumab Clearance and Functional Assays after Stopping Treatment During the study period, the primary nephrologist for two patients decided to stop ravulizumab therapy. Data for both patients are presented in Fig. 2 . Given that two equivalent doses at the same dosing interval were not administered, the seven levels collected after weaning therapy were not included in the analyses of stable trough levels. Patient 5 had Shiga toxin-producing Escherichia coli (STEC) HUS with anuric acute kidney injury needing prolonged dialysis at an outside hospital. During this hospitalization, she received eculizumab initially, before changing to ravulizumab 600 mg every 4 weeks in accordance with a SR. She was referred to our institution for second opinion due to residual chronic kidney disease and proteinuria. Ravulizumab was discontinued as the patient had negative genetic panel except a benign variant of CFI and kidney biopsy showed scarring and interstitial fibrosis without TMA. After ravulizumab was discontinued, ravulizumab serum levels and AH50 levels was performed at regular intervals, starting at the time when the first missed dose would have been administered. A negative correlation was demonstrated between ravulizumab drug levels and time on a logarithmic scale (p = 0.0001) and estimated elimination half-life was 4.8 weeks. Ravulizumab levels exceeded 175 mcg/mL for greater than 8 weeks after last ravulizumab dose on a SR. AH50 remained undetectable at each check where ravulizumab levels exceeded 175 mcg/mL and remained < 10% for at least 8 weeks after last ravulizumab dose. A correlation between time and AH50 level could not be assessed as only three measurements exceed the lower limit of detection of 10% for the AH50 assay. Patient 8, with no known genetic mutations, was maintained on a MR of ravulizumab 300 mg every 4 weeks and had planned to start weaning therapy after being in remission for 12 months. Ravulizumab was gradually reduced by extending the dosing interval by two additional weeks with each dose. Ravulizumab trough and AH50 levels continued to be collected prior to the following dose. Patient 8 was receiving a MR due to his weight gain while receiving ravulizumab therapy. As intended to start weaning therapy, ravulizumab dose was not increased from 300 mg to 600 mg. Despite the lower dose, Patient 8 continued to have appropriate ravulizumab trough levels prior to extending the dosing interval. After extending the dosing interval, Patient 8 continued to have ravulizumab trough levels exceeding 175 mcg/mL at both 6 and 8 weeks after last ravulizumab dose. Ravulizumab levels were below 175 mcg/mL threshold at 10 weeks after the next ravulizumab dose. AH50 levels remained undetectable at each check during study period. Selected Safety Parameters Reported side effects since initiation of ravulizumab are reported in Table 3 . The most frequently reported side effects in the cohort were infectious events (67%), fatigue (56%), headaches (33%), and diarrhea (33%) with no significant difference observed between the SR and MR groups. Online Resource 2 describes the rate of pADE by average trough quartile. All the patients in the cohort were receiving prophylaxis for meningococcal infections, had completed primary series of childhood meningococcal, pneumococcal and Haemophilus influenzae vaccinations and were on an established antihypertensive regimen at the time of ravulizumab initiation. However, shortly after the start of ravulizumab, two patients self-discontinued their antihypertensive regimen and were admitted for hypertensive emergency (Patients 4 and 6). Blood pressure normalized after resuming home anti-hypertensive medications. Table 3 Frequency of possible adverse drug events across dosing groups. Values presented as number of patients and corresponding percentages. (ULN, upper limit of normal) Variable Standard regimen Modified Regimen P -value* Headache 3 (60) 0 (0) 0.17 Hypertensive urgency 1 (20) 1 (25) > 0.99 Infectious diseases 4 (80) 2 (50) 0.52 Diarrhea 2 (40) 1 (25) > 0.99 Fatigue 2 (40) 3 (75) 0.52 Alopecia 0 (0) 0 (0) > 0.99 Dizziness 1 (20) 0 (0) > 0.99 Infusion Site Reaction 0 (0) 0 (0) > 0.99 Elevated transaminases (> 3x ULN) 0 (0) 0 (0) > 0.99 *P < 0.05 from Fisher’s Exact Test. DISCUSSION This is the first study reporting ravulizumab trough levels in a pediatric cohort with aHUS. The ravulizumab trough levels in this cohort were slightly lower than those previously reported in phase-3 trials, but all exceeded the recommended efficacy threshold of 175 mcg/mL [ 19 ]. In addition, all patients achieved undetectable AH50 at these doses and no patients had aHUS relapse during the study period. Intra-patient variability was low and interpatient variability was consistent with previous reports for the cohort and SR/MR subgroups [ 18 – 19 ]. The predictability of ravulizumab trough levels for each patient and the variation in ravulizumab trough levels between patients provide further support for using this pharmacokinetic marker in the development of individualized dosing regimens. The mean ravulizumab trough level was higher for the MR group than the SR group, although statistically not significant. During the study period, one patient had ravulizumab therapy discontinued and one patient had ravulizumab slowly weaned off. Both patients demonstrated therapeutic ravulizumab trough levels and undetectable AH50 when checked at longer intervals of 6 weeks and 8 weeks after last ravulizumab dose. Individualized treatment schedules for C5 inhibitors may offer a chance to provide adequate complement suppression while minimizing risks of adverse events and drug costs. This report is the first to show that patients with aHUS continue to maintain low AH50 values and therapeutic ravulizumab levels with lower ravulizumab doses. These findings are consistent with reports in eculizumab, in which multiple reports have proposed alternative dosing strategies as an area of cost minimization [ 12 – 18 ]. For patients who require long-term anti-complement therapy, ravulizumab’s extended dosing interval is advantageous over eculizumab to reduce infusion center visits, direct drug costs and overall burden of care [ 1 , 23 ]. If there is a possibility of reducing ravulizumab dosing to below the FDA-recommended regimen, then direct cost savings will increase. Due to retrospective study design, we were unable to obtain actual cost data for the medication acquisition for each individual patient and dose. However, based on the wholesale acquisition cost of $ 21.30 per milligram of ravulizumab at this time, patients receiving a MR in this cohort had an average estimated cost savings of $ 81,183/patient/year (range $ 41,632 to $ 116,571). Future studies should explore direct and indirect costs of using modified dosing regimens. Additionally, this is the first individualized treatment schedule in pediatric patients with aHUS. Pediatric patients may be more susceptible to adverse events, mainly infection-related complications, from excessive complement inhibition. While our study did not show higher rates of pADE in patients with higher ravulizumab levels, the small sample size and limited period supports further investigation. The main limitation of this study is the retrospective and observational design. While many patients are currently receiving a MR, the ways in which a dosing regimen deviates from the SR and reasons for modification differ. This limits the ability to make direct comparisons between the two groups. An additional limitation is the small sample size available for analysis due to the rarity of pediatric aHUS. While the sample size for this study is small (N = 9), the sample size for the trial supporting FDA approval (N = 10) was as well [ 8 ]. Therefore, the ravulizumab trough levels in this cohort effectively doubles what has been published in the pediatric aHUS population. Lastly, this study does not explore either a target ravulizumab trough or AH50 level to maintain aHUS remission. Complement activity can be monitored in multiple ways (e.g. CH50, AH50, SC5b9, or C5). AH50 was selected as the preferred marker for patients receiving ravulizumab based on prior comparative studies [ 20 , 22 ]. Wilrich et al, demonstrated complete complement inhibition (AH50 of 0%) at ravulizumab concentrations above 200 mcg/mL, which aligned with expected therapeutic concentrations from clinical trials [ 22 ]. However, it is not known if aHUS remission can be maintained at higher AH50 activity. Other studies have reported aHUS remission in adults with higher CH50 target goals [ 13 – 14 ]. In conclusion, individualized maintenance regimens of ravulizumab based on TDM parameters, such as trough and/or AH50 levels is a promising area for further investigation. In this small pediatric cohort, patients on either SR or MR maintained ravulizumab trough levels above the accepted therapeutic threshold and achieved complete complement suppression. Patients on a MR were able to maintain disease control while also minimizing drug exposure and drug costs. With more studies evaluating the use of TDM with ravulizumab, a more streamlined approach can be formulated to generalize dosing regimen modifications. Declarations Disclosures The authors declare no conflicts or financial interest in any product or service mentioned in the manuscript, including grants, equipment, medications, employment, gifts, and honoraria. Each author contributed important intellectual content during manuscript drafting or revision and agrees to be personally accountable for the individual’s own contributions and to ensure that questions pertaining to the accuracy or integrity of any portion of the work, even one in which the author was not directly involved, are appropriately investigated and resolved, including with documentation in the literature if appropriate. Funding No funding was used to perform this research Ethics Approval Institutional Review Board approval was obtained from Baylor College of Medicine (Protocol H-54545) and Affiliated Institutions. Reporting of this study is in accordance with the Strengthening the Reporting of Observational studies in Epidemiology (STROBE) statement and Declaration of Helsinki. Consent to participate A waiver of consent and publishing was approved by the Baylor College of Medicine (Protocol H-54545) given the retrospective nature of the study with minimal risk to patients. Material Re-Use Scientific abstract and poster was presented at American Society of Nephrology (ASN) Kidney Week 2024. Research Resource Identifiers Software: GraphPad Prism (RRID:SCR_002798) Author Contributions Conceptualization: Samara M. Mendez Nunez, Samantha Brokenshire, Poyyapakkam Srivaths, Joseph Angelo, Shweta Shah, Mini Michael; Data Curation: Samara M. Mendez Nunez, Samantha Brokenshire; Formal Analysis: Samara M. Mendez Nunez, Samantha Brokenshire, Poyyapakkam Srivaths, Joseph Angelo, Shweta Shah, Mini Michael; Funding acquisition: Not applicable; Investigation: Samara M. Mendez Nunez, Samantha Brokenshire; Methodology: Samara M. Mendez Nunez, Samantha Brokenshire, Poyyapakkam Srivaths, Joseph Angelo, Shweta Shah, Mini Michael; Project administration: Samara M. Mendez Nunez, Samantha Brokenshire; Resources: Not applicable; Software: Samara M. Mendez Nunez; Supervision: Samantha Brokenshire, Mini Michael; Validation: Samara M. Mendez Nunez, Samantha Brokenshire; Visualization: Samara M. Mendez Nunez, Samantha Brokenshire; Writing – original draft: Samara M. Mendez Nunez, Samantha Brokenshire; Writing – review & editing: Poyyapakkam Srivaths, Joseph Angelo, Shweta Shah, Mini Michael. References Michael M, Bagga A, Sartain SE, Smith RJH (2022) Haemolytic uraemic syndrome. 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Gatault P, Brachet G, Ternant D, Degenne D, Récipon G, Barbet C, Gyan E, Gouilleux-Gruart V, Bordes C, Farrell A, Halimi JM, Watier H (2015) Therapeutic drug monitoring of eculizumab: Rationale for an individualized dosing schedule. Mabs 7(6):1205-11. https://doi.org/10.1080/19420862.2015.1086049 Willrich MAV, Andreguetto BD, Sridharan M, Fervenza FC, Tostrud LJ, Ladwig PM, Rivard AM, Hetrick MD, Olson RN, Bryant SC, Snyder MR, Murray DL (2018) The impact of eculizumab on routine complement assays. J Immunol Methods 460:63-71. https://doi.org/10.1016/j.jim.2018.06.010. Wijnsma KL, Duineveld C, Wetzels JFM, van de Kar NCAJ (2019) Eculizumab in atypical hemolytic uremic syndrome: strategies toward restrictive use. Pediatr Nephrol 34(11):2261-2277. https://doi.org/10.1007/s00467-018-4091-3. Erratum in: (2019) Pediatr Nephrol 34(4):741-742. https://doi.org/10.1007/s00467-018-4186-x. Sridharan M, Go RS, Willrich MAV (2022) Clinical utility and potential cost savings of pharmacologic monitoring of eculizumab for complement-mediated thrombotic microangiopathy. Mayo Clin Proc Innov Qual Outcomes 6(5):458-464. https://doi.org/10.1016/j.mayocpiqo.2022.03.005. Erratum in: (2024) Mayo Clin Proc Innov Qual Outcomes 11;8(5):480. https://doi.org/10.1016/j.mayocpiqo.2024.06.004. Ter Avest M, Langemeijer SMC, Schols SEM, Burger DM, van de Kar NCAJ, Blijlevens NMA, Kievit W, Ter Heine R (2021) The potential of individualized dosing of ravulizumab to improve patient-friendliness of paroxysmal nocturnal haemoglobinuria treatment at reduced costs. Br J Clin Pharmacol 87(8):3359-3363. https://doi.org/10.1111/bcp.14748. Cataland S, Ariceta G, Chen P, Dixon B (2019) Discordance between free C5 and CH50 complement assays in measuring complement C5 inhibition in patients with aHUS treated with ravulizumab. Blood 134(Supplement_1):1099. https://doi.org/10.1182/blood-2019-122421 Sahelijo L, Mujeebuddin A, Mitchell D, Larouche R. First in human single ascending dose study: safety, biomarker, pharmacokinetics and exposure-response relationships of ALXN1210, a humanized monoclonal antibody to C5, with marked half-life extension and potential for significantly longer dosing intervals. In: American Society of Hematology Washington, DC, 2015. Willrich MAV, Ladwig PM, Martinez MA, Sridharan MR, Go RS, Murray DL; Complement Alternative Pathway Thrombotic Microangiopathy (CAP-TMA) Disease Oriented Group at the Mayo Clinic (2021) Monitoring ravulizumab effect on complement assays. J Immunol Methods 490:112944. https://doi.org/10.1016/j.jim.2020.112944. Ladwig PM, Barnidge DR, Willrich MA (2017) Quantification of the igg2/4 kappa monoclonal therapeutic eculizumab from serum using isotype specific affinity purification and microflow lc-esi-q-tof mass spectrometry. J Am Soc Mass Spectrom 28(5):811-817. https://doi.org/10.1007/s13361-016-1566-y. Tomazos I, Hatswell AJ, Cataland S, Chen P, Freemantle N, Lommele Å, Deighton K, Knowles E, Sheerin NS, Rondeau E (2022) Comparative efficacy of ravulizumab and eculizumab in the treatment of atypical hemolytic uremic syndrome: An indirect comparison using clinical trial data. Clin Nephrol 97(5):261-272. https://doi.org/10.5414/CN110516. Flynn JT, Kaelber DC, Baker-Smith CM, Blowey D, Carroll AE, Daniels SR, de Ferranti SD, Dionne JM, Falkner B, Flinn SK, Gidding SS, Goodwin C, Leu MG, Powers ME, Rea C, Samuels J, Simasek M, Thaker VV, Urbina EM; SUBCOMMITTEE ON SCREENING AND MANAGEMENT OF HIGH BLOOD PRESSURE IN CHILDREN (2017) Clinical practice guideline for screening and management of high blood pressure in children and adolescents. Pediatrics 140(3):e20171904. https://doi.org/10.1542/peds.2017-1904. Erratum in: (2017) Pediatrics 140(6):e20173035. https://doi.org/10.1542/peds.2017-3035. Erratum in: (2018) Pediatrics 142(3):e20181739. https://doi.org/10.1542/peds.2018-1739. PMID: 28827377. Ter Avest M, Steenbreker H, Bouwmeester RN, Duineveld C, Wijnsma KL, van den Heuvel LPWJ, Langemeijer SMC, Wetzels JFM, van de Kar NCAJ, Ter Heine R; CUREiHUS Study Group (2023) Proteinuria and exposure to eculizumab in atypical hemolytic uremic syndrome. Clin J Am Soc Nephrol 18(6):759-766. https://doi.org/10.2215/CJN.0000000000000145. Bouwmeester RN, Ter Avest M, Wijnsma KL, Duineveld C, Ter Heine R, Volokhina EB, Van Den Heuvel LPWJ, Wetzels JFM, van de Kar NCAJ. (2021) Case report: Variable pharmacokinetic profile of eculizumab in an aHUS patient. Front Immunol 11:612706. https://doi.org/10.3389/fimmu.2020.612706. Supplementary Files PediatricNephrologyESM1.pdf PediatricNephrologyESM2.pdf Cite Share Download PDF Status: Published Journal Publication published 10 Jan, 2026 Read the published version in Pediatric Nephrology → Version 1 posted Editorial decision: Major Revisions Needed 02 Sep, 2025 Reviewers agreed at journal 04 Aug, 2025 Reviewers invited by journal 29 Jul, 2025 Editor assigned by journal 29 Jul, 2025 First submitted to journal 25 Jul, 2025 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. 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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-7216678","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":492843999,"identity":"f2828f8d-85b4-45aa-93ef-ed8a7c9b0457","order_by":0,"name":"Samara M Mendez Nunez","email":"","orcid":"","institution":"Texas Children's Hospital","correspondingAuthor":false,"prefix":"","firstName":"Samara","middleName":"M Mendez","lastName":"Nunez","suffix":""},{"id":492844000,"identity":"978bb06b-2f3d-48ad-a3c4-8821f2c7aec6","order_by":1,"name":"Samantha A Brokenshire","email":"data:image/png;base64,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","orcid":"https://orcid.org/0000-0002-7373-3542","institution":"Texas Children's Hospital","correspondingAuthor":true,"prefix":"","firstName":"Samantha","middleName":"A","lastName":"Brokenshire","suffix":""},{"id":492844001,"identity":"c7f81351-6273-432d-8938-302da8dd74c8","order_by":2,"name":"Poyyapakkam Srivaths","email":"","orcid":"","institution":"Baylor College of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Poyyapakkam","middleName":"","lastName":"Srivaths","suffix":""},{"id":492844002,"identity":"128af7b3-c9c0-4a41-a9d0-2d9697ff7dea","order_by":3,"name":"Joseph Angelo","email":"","orcid":"","institution":"Baylor College of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Joseph","middleName":"","lastName":"Angelo","suffix":""},{"id":492844003,"identity":"3093a392-9a80-4dfb-bba9-72253587cd36","order_by":4,"name":"Shweta Shah","email":"","orcid":"","institution":"Baylor College of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Shweta","middleName":"","lastName":"Shah","suffix":""},{"id":492844004,"identity":"889f914f-c9a2-49e1-b782-168c70770b2f","order_by":5,"name":"Mini Michael","email":"","orcid":"","institution":"Baylor College of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Mini","middleName":"","lastName":"Michael","suffix":""}],"badges":[],"createdAt":"2025-07-25 18:30:41","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7216678/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7216678/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00467-025-07113-5","type":"published","date":"2026-01-10T15:58:52+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":88349548,"identity":"5493f3d5-411b-4c54-a91d-7a605a076884","added_by":"auto","created_at":"2025-08-05 14:06:06","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":126027,"visible":true,"origin":"","legend":"\u003cp\u003eIndividual ravulizumab trough levels by dosing regimen. Each patient’s mean trough level is represented by solid dark lines. Dosing groups are indicated by symbol: standard regimen (white circles, Patient 1-5) and modified regimen (black squares. Patient 6-9). The recommended target ravulizumab trough level is shown as a dashed red line\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7216678/v1/04b7c84af2fb6d3f651754da.png"},{"id":88348028,"identity":"3c82c124-73c0-4f16-a35c-863ba78a3b87","added_by":"auto","created_at":"2025-08-05 13:58:06","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":307202,"visible":true,"origin":"","legend":"\u003cp\u003eRavulizumab trough levels (black squares) and AH50 activity (white circles) following either discontinuation (a. Patient 5) or dose weaning (b. Patient 8), based on individualized regimens determined by the primary nephrologist (doses indicated by black arrows). Due to the assay’s lower detection limit, AH50 values below 10% could not be quantified and are marked with an asterisk (*). The recommended target ravulizumab trough level is shown as a dashed red line, and the AH50 suppression threshold is indicated by a dashed blue line\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7216678/v1/69354fb05fcf8431b9959653.png"},{"id":100070018,"identity":"657b6190-2909-4084-ba6a-83cce8fcb622","added_by":"auto","created_at":"2026-01-12 16:15:55","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1128523,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7216678/v1/f6eebc5e-d7b3-4b17-89b6-bd2c46e613f3.pdf"},{"id":88349553,"identity":"de72534a-4dd4-4284-8d7e-714b6585d7dd","added_by":"auto","created_at":"2025-08-05 14:06:06","extension":"pdf","order_by":9,"title":"","display":"","copyAsset":false,"role":"supplement","size":707475,"visible":true,"origin":"","legend":"","description":"","filename":"PediatricNephrologyESM1.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7216678/v1/b37ee308e8e16521a7e5aebe.pdf"},{"id":88350576,"identity":"7b2381bd-0113-44bb-8ae7-0477030129a0","added_by":"auto","created_at":"2025-08-05 14:14:06","extension":"pdf","order_by":10,"title":"","display":"","copyAsset":false,"role":"supplement","size":124614,"visible":true,"origin":"","legend":"","description":"","filename":"PediatricNephrologyESM2.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7216678/v1/b6dfafe1b0976b315da935e6.pdf"}],"financialInterests":"","formattedTitle":"Evaluation of Ravulizumab Trough Levels in Pediatric Atypical Hemolytic Uremic Syndrome in Remission","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eRavulizumab is a long-acting complement inhibitor indicated for the treatment of atypical hemolytic uremic syndrome (aHUS), a rare variant of thrombotic microangiopathy associated with uncontrolled activation of the alternative complement pathway [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e–\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Ravulizumab binds to complement protein C5, thereby preventing the generation of the terminal complex C5b-9 (Membrane Attack Complex, MAC) and subsequent complement-mediated endothelial damage [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e–\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Ravulizumab was derived from modifications to the backbone of eculizumab which reduces endosomal degradation, increases elimination half-life by four-fold and extends dosing interval to every 4–8 weeks based on a FDA-approved, weight-based dosing scheme [\u003cspan additionalcitationids=\"CR6 CR7 CR8 CR9\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e–\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIndividualized anti-complement dosing regimens based on therapeutic drug monitoring (TDM), markers of complement activity, or a combination of both have been suggested in response to high medication costs, frequent infusions visits, and serious safety concerns for long-term complement suppression [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Published reports in aHUS have been limited to pharmacokinetic models or a small number of patients receiving eculizumab [\u003cspan additionalcitationids=\"CR13 CR14 CR15 CR16 CR17\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e–\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Only one pharmacokinetic–pharmacodynamic simulation model has been published for ravulizumab and was designed to reflect patients with paroxysmal nocturnal hemoglobinuria [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. No real-world studies have been reported in pediatrics.\u003c/p\u003e\u003cp\u003eRationale for these modified dosing strategies for eculizumab and ravulizumab stems from a robust exposure-response relationship and mean trough concentrations which exceed previously established efficacy thresholds [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan additionalcitationids=\"CR21\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e–\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Alexion Pharmaceuticals, Inc reports that ravulizumab trough concentrations \u0026gt; 175 mcg/mL result in complete complement blockade, defined as free C5 \u0026lt; 0.5 mcg/mL [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. However, the observed mean (coefficient of variation, %CV) ravulizumab serum trough concentration at the approved dose in the maintenance phase in phase III clinical trials were 507 (42.5), 683 (46.1), and 549 (34.1) mcg/mL for adult (N = 46), children \u0026lt; 20 kg (N = 7) and children ≥ 20 to \u0026lt; 40 kg (N = 6), respectively [\u003cspan additionalcitationids=\"CR7 CR8\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e–\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. This exposure is nearly three-times higher than the recommended therapeutic threshold, suggesting patients could be at increased risk for dose-dependent adverse events and may be able to maintain adequate drug coverage with lower doses. However, the small number of pediatric patients included in the phase III clinical trial (N = 10) limits one’s ability to extrapolate these results to a larger population [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Additionally, the free C5 assay used in these trials is not readily available clinically to confirm adequate complement blockade in patients with aHUS treated with complement inhibitors [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Functional assays, including AH50 and CH50, which are commonly used in clinical practice were not included in major studies on ravulizumab for aHUS [\u003cspan additionalcitationids=\"CR6 CR7 CR8\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e–\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThis study serves to describe ravulizumab trough levels and corresponding AH50 in a pediatric cohort of aHUS in remission, exploring (1) the difference of ravulizumab trough levels for patients receiving standard regimen (SR) compared to TDM-guided, modified regimen (MR), (2) the intra-individual variability in serum trough levels on stable ravulizumab dose, (3) the percentage of patients with incomplete complement suppression, defined as AH50 ≥ 10% (4) the rates of possible adverse drug events (pADE) for patients with higher serum trough levels, and (5) the trend of serum trough and AH50 levels after discontinuing therapy.\u003c/p\u003e"},{"header":"METHODS","content":"\u003cp\u003e\u003cb\u003eStudy Design and Setting\u003c/b\u003e\u003c/p\u003e\u003cp\u003eWe performed a single-center, retrospective cohort study of pediatric patients with documented aHUS receiving outpatient ravulizumab infusions between June 30, 2023 and March 31, 2024. Study procedures were limited to medical record review. Institutional Review Board approval was obtained from Baylor College of Medicine (Protocol H-54545). A waiver of consent was approved given the retrospective nature of the study with minimal risk to patients. Reporting of this study is in accordance with the Strengthening the Reporting of Observational studies in Epidemiology (STROBE) statement and Declaration of Helsinki.\u003c/p\u003e\u003cp\u003e\u003cb\u003eParticipants and Study Size\u003c/b\u003e\u003c/p\u003e\u003cp\u003eEligible patients were \u0026lt; 18 years old and had a documented diagnosis of complement-mediated atypical aHUS, received at least two equal maintenance doses of ravulizumab before the end of study period, and had at least one ravulizumab trough level and one AH50 activity level recorded since ravulizumab initiation. AH50 was selected as the preferred functional assay for complement activity as it has been shown to consistently reflect decreased complement activity with increasing concentrations of ravulizumab and align with clinical trials in expected exposure-response relationship [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Patients who had documented laboratory signs consistent with active aHUS (platelet count \u0026lt; 150,000/mm\u003csup\u003e3\u003c/sup\u003e or lactate dehydrogenase (LDH) \u0026gt; 1.5x upper normal limit) since June 30, 2023 were excluded.\u003c/p\u003e\u003cp\u003e\u003cb\u003eData Sources\u003c/b\u003e\u003c/p\u003e\u003cp\u003eData on patient demographic characteristics, past medical history, medication history, laboratory tests, and vital signs were obtained from electronic medical record (EMR) at the end of the study period. Selected laboratory results, including ravulizumab trough levels and AH50 activity levels, were obtained through laboratory services from Mayo Clinic Laboratories. AH50 assays are performed by ELISA through the measurement of the proprietary detection antibody targeting MAC [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Any pADE was obtained through review of clinical notes from in-person and telephonic consultations, infusion visits, or hospital admissions and the clinical problem list documented in the EMR.\u003c/p\u003e\u003cp\u003e\u003cb\u003eExposures and Outcomes\u003c/b\u003e\u003c/p\u003e\u003cp\u003eAll patients received maintenance ravulizumab infusions at the discretion of their primary nephrologist. Ravulizumab exposure was evaluated using the serum trough level drawn after at least two equal maintenance doses. At the time of each trough level, the patient’s ravulizumab dosing regimen was classified as SR or MR. SR was defined as ravulizumab dose and dosing interval that matched the package insert for the patient’s weight at that time. MR was selected if their dose or dosing interval differed from the package insert. Rationale for selecting a MR was also collected if described in the EMR.\u003c/p\u003e\u003cp\u003eThe primary objective was to describe troughs and corresponding AH50 for pediatric patients with aHUS on a stable ravulizumab regimen. For the purposes of this study, adequate complement suppression was defined as AH50 \u0026lt; 10% [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. If a patient had ravulizumab discontinued during the study period, all ravulizumab levels and AH50 were collected until the end of the study period. Additional laboratory markers, including CH50, SC5b9, LDH, haptoglobin, and urine protein-to-creatinine ratio (UPC), were collected as available (Online Resource 1) but not included in primary analyses. This study sought to determine if higher ravulizumab exposure was associated with higher rates of pADE. Side effects evaluated included documented new or worsening headaches, diarrhea, fatigue, alopecia, dizziness, infusion site reactions, increased transaminases, hypertensive urgency, and infections requiring antibiotics or hospital admission. These pADE were selected after reviewing common or serious adverse reactions reported in the package insert or case reports [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. When appropriate, side effects were defined using the Common Terminology Criteria for Adverse Events (CTCAE) version 5.0. Hypertensive urgency was defined as a blood pressure (BP) of ≥ 30 mmHg above the 95th percentile in children or a BP \u0026gt; 180/120 mmHg in adolescents requiring intermittent anti-hypertensive medications for BP control [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003cb\u003eStatistical Analyses\u003c/b\u003e\u003c/p\u003e\u003cp\u003eContinuous variables were presented as means with standard deviations and categorical variables as frequencies with percentages. Normal distribution was assessed using the Shapiro-Wilk test. Nested t-test was used to compare the mean ravulizumab trough levels between dosing regimens. The assessment of the intra-patient variability of ravulizumab trough levels was done descriptively and through the paired t-test, using the first two trough levels for patients with multiple levels collected on the same dosing regimen. Pearson correlation was used to test the relationship between ravulizumab drug levels and AH50. The comparison of the incidence of pADE was performed using the Fisher’s Exact test. A post-hoc power analysis was not conducted.\u003c/p\u003e"},{"header":"RESULTS","content":"\u003cp\u003e\u003cb\u003ePatient Selection and Descriptive Data\u003c/b\u003e\u003c/p\u003e\u003cp\u003eTwelve patients receiving outpatient ravulizumab were screened for eligibility. Nine patients, of which 27 drug levels resulted, were included. All excluded patients were receiving ravulizumab for an alternative indication (n\u0026thinsp;=\u0026thinsp;2 with C3 glomerulopathy, n\u0026thinsp;=\u0026thinsp;1 with paroxysmal nocturnal hemoglobinuria). Baseline characteristics and ravulizumab dosing regimens are reported in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Seven patients had complement gene mutations identified (n\u0026thinsp;=\u0026thinsp;2 with \u003cem\u003eCFH\u003c/em\u003e mutation, n\u0026thinsp;=\u0026thinsp;2 with \u003cem\u003eC3\u003c/em\u003e gene mutation, n\u0026thinsp;=\u0026thinsp;1 with \u003cem\u003eCFHR1\u003c/em\u003e homozygous deletion, n\u0026thinsp;=\u0026thinsp;1 with \u003cem\u003eCFI\u003c/em\u003e variant of unknown significance, and n\u0026thinsp;=\u0026thinsp;1 with Factor H autoantibody associated with \u003cem\u003eCFHR3/CFHR1\u003c/em\u003e and \u003cem\u003eCFHR1/CFHR4\u003c/em\u003e deletion). Ravulizumab was continued for Patient 2 due to elevated Factor H autoantibodies (mean 90.1 units/mL [SD 16.9] during study period, normal\u0026thinsp;\u0026lt;\u0026thinsp;22 units/mL). The median age and weight at the start of ravulizumab use was 4.3 years (IQR 2.2\u0026ndash;13.4) and 17.8 kg (IQR 12-39.3), respectively. At the time the first trough was measured, the median weight was 19.1 kg (IQR 14.6\u0026ndash;50.8). Five patients were receiving maintenance ravulizumab dosing defined as SR (Patients 1\u0026ndash;5). The other four patients were receiving a MR (Patients 6\u0026ndash;9), where dose was not increased for weight gain (n\u0026thinsp;=\u0026thinsp;4) and dosing interval was extended due to scheduling conflicts (n\u0026thinsp;=\u0026thinsp;1). Other documented rationale for MR included elevated troughs (n\u0026thinsp;=\u0026thinsp;4), clinical stability (n\u0026thinsp;=\u0026thinsp;4), and concern for pADE (n\u0026thinsp;=\u0026thinsp;1). No patients were receiving kidney replacement therapy at the initiation of ravulizumab or during the study period. Proteinuria, assessed using UPC, was included as a surrogate marker to explain potential urinary ravulizumab losses [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Seven of the patients had proteinuria, defined as median UPC\u0026thinsp;\u0026ge;\u0026thinsp;0.2 mg/mg, during the study period (Online Resource 1). Two patients had severe proteinuria, defined as median UPC\u0026thinsp;\u0026gt;\u0026thinsp;2 mg/mg (Patient 5, UPC 7.1 [IQR 5.7\u0026ndash;11.3] and Patient 7, UPC 3 mg/mg [IQR 2.2\u0026ndash;4.3]). Both patients had Stage III acute kidney injury, requiring prolonged dialysis, at initial aHUS presentation. Kidney biopsies completed after systemic signs of aHUS had resolved showed chronic changes and scarring. All patients within the cohort had normal serum albumin and none were suspected to have isolated renal thrombotic microangiopathy.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eBaseline patient characteristics at the time of the first ravulizumab trough level measurement collection. \u003cem\u003e(C3, complement component 3; CFH, complement factor H; CFHR1, complement factor H related 1, CFHR3, complement factor H related 3; CFHR4, complement factor H related 4; CFI, complement factor I; F, female; M, male; MR, maintenance regimen; SR, standard regimen)\u003c/em\u003e\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"9\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eID\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSex\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eComplement Gene Mutation\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eAge (years)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eWeight (kg)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eRavulizumab Regimen\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eTime on current regimen (years)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eTotal time on ravulizumab (years)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003eDosing Regimen\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eCFH\u003c/em\u003e\u003c/p\u003e\u003cp\u003e\u003cem\u003eCFHR3/CFHR1\u003c/em\u003e, homozygous deletion\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e15.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e600 mg every 4 weeks\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e2.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e2.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003eSR\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eCFHR3/CFHR1\u003c/em\u003e deletion\u003c/p\u003e\u003cp\u003e\u003cem\u003eCFHR1/CFHR4\u003c/em\u003e deletion\u003c/p\u003e\u003cp\u003eFHAA\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e17.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e55.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e3000 mg every 8 weeks\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e4.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e4.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003eSR\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eCFHR1\u003c/em\u003e homozygous deletion\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e6.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e19.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e600 mg every 4 weeks\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e1.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e1.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003eSR\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eNone\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e60.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e3300 mg every 8 weeks\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003eSR\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eCFI\u003c/em\u003e variant of unknown significance\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e14.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e600 mg every 4 weeks\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003eSR\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eC3\u003c/em\u003e\u003c/p\u003e\u003cp\u003e\u003cem\u003eCFHR3/CFHR1\u003c/em\u003e, heterozygous deletion\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e16.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e50.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e2700 mg every 8 weeks\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e1.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e1.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003eMR\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eCFH\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e11.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e300 mg every 4 weeks\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003eMR\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eNone\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e10.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e300 mg every 4 weeks\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003eMR\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eC3\u003c/em\u003e\u003c/p\u003e\u003cp\u003e\u003cem\u003eCFHR3/CFHR1\u003c/em\u003e, homozygous deletion\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e10.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e41.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e2700 mg every 10 weeks\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e1.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e1.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003eMR\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eRavulizumab Pharmacokinetics and Functional Assays\u003c/b\u003e\u003c/p\u003e\u003cp\u003eRavulizumab trough levels drawn while patients were receiving stable maintenance regimens (n\u0026thinsp;=\u0026thinsp;20) and corresponding laboratory measures are shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The mean ravulizumab trough level of the entire cohort was 399.1\u0026thinsp;\u0026plusmn;\u0026thinsp;107.3 mcg/mL, with all the levels above the goal of 175 mcg/mL. The mean ravulizumab trough levels for patients on SR and MR were 363.7\u0026thinsp;\u0026plusmn;\u0026thinsp;114.1 mcg/mL and 434.6\u0026thinsp;\u0026plusmn;\u0026thinsp;92.1 mcg/mL, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Both patients with severe proteinuria had mean trough levels above the cohort\u0026rsquo;s mean. No statistical difference was observed in the trough levels between groups (p\u0026thinsp;=\u0026thinsp;0.67). The mean coefficient of variation in the six patients with multiple levels collected was reported below 25% (7.8\u0026thinsp;\u0026plusmn;\u0026thinsp;7.4%). Additionally, a non-significant statistical difference was observed between the first and second trough levels collected in those six patients (p\u0026thinsp;=\u0026thinsp;0.89).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eRavulizumab trough levels and AH50 levels description. Results for trough levels are mean\u0026thinsp;\u003cb\u003e\u0026plusmn;\u003c/b\u003e\u0026thinsp;SD. Detection limit of AH50 activity level test is \u0026lt;\u0026thinsp;10% \u003cem\u003e(CV, coefficient of variation; MR, maintenance regimen; SD, standard deviation; SR, standard regimen)\u003c/em\u003e\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"8\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eNumber of troughs\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eRavulizumab trough level (mcg/mL)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eRange\u003c/p\u003e\u003cp\u003e(mcg/mL)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eCV\u003c/p\u003e\u003cp\u003e(%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eAH50\u003c/p\u003e\u003cp\u003e(%)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e\u003cp\u003e\u003cb\u003eTotal (N\u0026thinsp;=\u0026thinsp;9)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e20\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cb\u003e399.1 (107.3)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e232.5\u0026ndash;558\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u003cb\u003e26.9\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;10\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e\u003cb\u003eSR (n\u0026thinsp;=\u0026thinsp;5)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e10\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cb\u003e363.7 (114.1)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e232.5\u0026ndash;558\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u003cb\u003e31.4\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;10\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePatient 1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e263.5 (29.9)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e232.5\u0026ndash;286\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e11.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;10\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePatient 2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e541.5 (23.3)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e525\u0026ndash;558\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e4.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;10\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePatient 3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e289 (0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;10\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePatient 4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e412 (0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;10\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePatient 5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e399.3 (10.3)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e389-409.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e3.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;10\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e\u003cb\u003eMR (n\u0026thinsp;=\u0026thinsp;4)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003e10\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cb\u003e434.6 (92.1)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e304.3-545.9\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u003cb\u003e21.2\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;10\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePatient 6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e208 (27.7)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e484.3-545.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e5.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;10\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePatient 7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e437.9 (92.9)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e347-532.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e21.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;10\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePatient 8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e388 (0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;10\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePatient 9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e306.2 (2.6)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e304.3\u0026ndash;308\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;10\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eRavulizumab Clearance and Functional Assays after Stopping Treatment\u003c/b\u003e\u003c/p\u003e\u003cp\u003eDuring the study period, the primary nephrologist for two patients decided to stop ravulizumab therapy. Data for both patients are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Given that two equivalent doses at the same dosing interval were not administered, the seven levels collected after weaning therapy were not included in the analyses of stable trough levels.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003ePatient 5 had Shiga toxin-producing \u003cem\u003eEscherichia coli\u003c/em\u003e (STEC) HUS with anuric acute kidney injury needing prolonged dialysis at an outside hospital. During this hospitalization, she received eculizumab initially, before changing to ravulizumab 600 mg every 4 weeks in accordance with a SR. She was referred to our institution for second opinion due to residual chronic kidney disease and proteinuria. Ravulizumab was discontinued as the patient had negative genetic panel except a benign variant of CFI and kidney biopsy showed scarring and interstitial fibrosis without TMA. After ravulizumab was discontinued, ravulizumab serum levels and AH50 levels was performed at regular intervals, starting at the time when the first missed dose would have been administered. A negative correlation was demonstrated between ravulizumab drug levels and time on a logarithmic scale (p\u0026thinsp;=\u0026thinsp;0.0001) and estimated elimination half-life was 4.8 weeks. Ravulizumab levels exceeded 175 mcg/mL for greater than 8 weeks after last ravulizumab dose on a SR. AH50 remained undetectable at each check where ravulizumab levels exceeded 175 mcg/mL and remained\u0026thinsp;\u0026lt;\u0026thinsp;10% for at least 8 weeks after last ravulizumab dose. A correlation between time and AH50 level could not be assessed as only three measurements exceed the lower limit of detection of 10% for the AH50 assay.\u003c/p\u003e\u003cp\u003ePatient 8, with no known genetic mutations, was maintained on a MR of ravulizumab 300 mg every 4 weeks and had planned to start weaning therapy after being in remission for 12 months. Ravulizumab was gradually reduced by extending the dosing interval by two additional weeks with each dose. Ravulizumab trough and AH50 levels continued to be collected prior to the following dose. Patient 8 was receiving a MR due to his weight gain while receiving ravulizumab therapy. As intended to start weaning therapy, ravulizumab dose was not increased from 300 mg to 600 mg. Despite the lower dose, Patient 8 continued to have appropriate ravulizumab trough levels prior to extending the dosing interval. After extending the dosing interval, Patient 8 continued to have ravulizumab trough levels exceeding 175 mcg/mL at both 6 and 8 weeks after last ravulizumab dose. Ravulizumab levels were below 175 mcg/mL threshold at 10 weeks after the next ravulizumab dose. AH50 levels remained undetectable at each check during study period.\u003c/p\u003e\u003cp\u003e\u003cb\u003eSelected Safety Parameters\u003c/b\u003e\u003c/p\u003e\u003cp\u003eReported side effects since initiation of ravulizumab are reported in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The most frequently reported side effects in the cohort were infectious events (67%), fatigue (56%), headaches (33%), and diarrhea (33%) with no significant difference observed between the SR and MR groups. Online Resource 2 describes the rate of pADE by average trough quartile. All the patients in the cohort were receiving prophylaxis for meningococcal infections, had completed primary series of childhood meningococcal, pneumococcal and \u003cem\u003eHaemophilus influenzae\u003c/em\u003e vaccinations and were on an established antihypertensive regimen at the time of ravulizumab initiation. However, shortly after the start of ravulizumab, two patients self-discontinued their antihypertensive regimen and were admitted for hypertensive emergency (Patients 4 and 6). Blood pressure normalized after resuming home anti-hypertensive medications.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eFrequency of possible adverse drug events across dosing groups. Values presented as number of patients and corresponding percentages. \u003cem\u003e(ULN, upper limit of normal)\u003c/em\u003e\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eVariable\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eStandard regimen\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eModified Regimen\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003eP\u003c/em\u003e-value*\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eHeadache\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e3 (60)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0 (0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.17\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eHypertensive urgency\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1 (20)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1 (25)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u0026gt;\u0026thinsp;0.99\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eInfectious diseases\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e4 (80)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2 (50)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.52\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDiarrhea\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e2 (40)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1 (25)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u0026gt;\u0026thinsp;0.99\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFatigue\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e2 (40)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3 (75)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.52\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAlopecia\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0 (0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0 (0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u0026gt;\u0026thinsp;0.99\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDizziness\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1 (20)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0 (0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u0026gt;\u0026thinsp;0.99\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eInfusion Site Reaction\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0 (0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0 (0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u0026gt;\u0026thinsp;0.99\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eElevated transaminases (\u0026gt;\u0026thinsp;3x ULN)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0 (0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0 (0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u0026gt;\u0026thinsp;0.99\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e*P\u0026thinsp;\u0026lt;\u0026thinsp;0.05 from Fisher\u0026rsquo;s Exact Test.\u003c/p\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eThis is the first study reporting ravulizumab trough levels in a pediatric cohort with aHUS. The ravulizumab trough levels in this cohort were slightly lower than those previously reported in phase-3 trials, but all exceeded the recommended efficacy threshold of 175 mcg/mL [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. In addition, all patients achieved undetectable AH50 at these doses and no patients had aHUS relapse during the study period. Intra-patient variability was low and interpatient variability was consistent with previous reports for the cohort and SR/MR subgroups [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. The predictability of ravulizumab trough levels for each patient and the variation in ravulizumab trough levels between patients provide further support for using this pharmacokinetic marker in the development of individualized dosing regimens. The mean ravulizumab trough level was higher for the MR group than the SR group, although statistically not significant. During the study period, one patient had ravulizumab therapy discontinued and one patient had ravulizumab slowly weaned off. Both patients demonstrated therapeutic ravulizumab trough levels and undetectable AH50 when checked at longer intervals of 6 weeks and 8 weeks after last ravulizumab dose.\u003c/p\u003e\u003cp\u003eIndividualized treatment schedules for C5 inhibitors may offer a chance to provide adequate complement suppression while minimizing risks of adverse events and drug costs. This report is the first to show that patients with aHUS continue to maintain low AH50 values and therapeutic ravulizumab levels with lower ravulizumab doses. These findings are consistent with reports in eculizumab, in which multiple reports have proposed alternative dosing strategies as an area of cost minimization [\u003cspan additionalcitationids=\"CR13 CR14 CR15 CR16 CR17\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. For patients who require long-term anti-complement therapy, ravulizumab\u0026rsquo;s extended dosing interval is advantageous over eculizumab to reduce infusion center visits, direct drug costs and overall burden of care [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. If there is a possibility of reducing ravulizumab dosing to below the FDA-recommended regimen, then direct cost savings will increase. Due to retrospective study design, we were unable to obtain actual cost data for the medication acquisition for each individual patient and dose. However, based on the wholesale acquisition cost of \u003cspan\u003e$\u003c/span\u003e21.30 per milligram of ravulizumab at this time, patients receiving a MR in this cohort had an average estimated cost savings of \u003cspan\u003e$\u003c/span\u003e81,183/patient/year (range \u003cspan\u003e$\u003c/span\u003e41,632 to \u003cspan\u003e$\u003c/span\u003e116,571). Future studies should explore direct and indirect costs of using modified dosing regimens. Additionally, this is the first individualized treatment schedule in pediatric patients with aHUS. Pediatric patients may be more susceptible to adverse events, mainly infection-related complications, from excessive complement inhibition. While our study did not show higher rates of pADE in patients with higher ravulizumab levels, the small sample size and limited period supports further investigation.\u003c/p\u003e\u003cp\u003eThe main limitation of this study is the retrospective and observational design. While many patients are currently receiving a MR, the ways in which a dosing regimen deviates from the SR and reasons for modification differ. This limits the ability to make direct comparisons between the two groups. An additional limitation is the small sample size available for analysis due to the rarity of pediatric aHUS. While the sample size for this study is small (N\u0026thinsp;=\u0026thinsp;9), the sample size for the trial supporting FDA approval (N\u0026thinsp;=\u0026thinsp;10) was as well [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Therefore, the ravulizumab trough levels in this cohort effectively doubles what has been published in the pediatric aHUS population. Lastly, this study does not explore either a target ravulizumab trough or AH50 level to maintain aHUS remission. Complement activity can be monitored in multiple ways (e.g. CH50, AH50, SC5b9, or C5). AH50 was selected as the preferred marker for patients receiving ravulizumab based on prior comparative studies [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Wilrich et al, demonstrated complete complement inhibition (AH50 of 0%) at ravulizumab concentrations above 200 mcg/mL, which aligned with expected therapeutic concentrations from clinical trials [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. However, it is not known if aHUS remission can be maintained at higher AH50 activity. Other studies have reported aHUS remission in adults with higher CH50 target goals [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn conclusion, individualized maintenance regimens of ravulizumab based on TDM parameters, such as trough and/or AH50 levels is a promising area for further investigation. In this small pediatric cohort, patients on either SR or MR maintained ravulizumab trough levels above the accepted therapeutic threshold and achieved complete complement suppression. Patients on a MR were able to maintain disease control while also minimizing drug exposure and drug costs. With more studies evaluating the use of TDM with ravulizumab, a more streamlined approach can be formulated to generalize dosing regimen modifications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eDisclosures\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflicts or financial interest in any product or service mentioned in the manuscript, including grants, equipment, medications, employment, gifts, and honoraria. Each author contributed important intellectual content during manuscript drafting or revision and agrees to be personally accountable for the individual’s own contributions and to ensure that questions pertaining to the accuracy or integrity of any portion of the work, even one in which the author was not directly involved, are appropriately investigated and resolved, including with documentation in the literature if appropriate.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo funding was used to perform this research\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics Approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eInstitutional Review Board approval was obtained from Baylor College of Medicine (Protocol H-54545) and Affiliated Institutions. Reporting of this study is in accordance with the Strengthening the Reporting of Observational studies in Epidemiology (STROBE) statement and Declaration of Helsinki.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA waiver of consent and publishing was approved by the Baylor College of Medicine (Protocol H-54545) given the retrospective nature of the study with minimal risk to patients.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMaterial Re-Use\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eScientific abstract and poster was presented at American Society of Nephrology (ASN) Kidney Week 2024.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResearch Resource Identifiers\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSoftware: GraphPad Prism (RRID:SCR_002798)\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eConceptualization: Samara M. Mendez Nunez, Samantha Brokenshire, Poyyapakkam Srivaths, Joseph Angelo, Shweta Shah, Mini Michael; Data Curation: Samara M. Mendez Nunez, Samantha Brokenshire; Formal Analysis: Samara M. Mendez Nunez, Samantha Brokenshire, Poyyapakkam Srivaths, Joseph Angelo, Shweta Shah, Mini Michael; Funding acquisition: Not applicable; Investigation: Samara M. Mendez Nunez, Samantha Brokenshire; Methodology: Samara M. Mendez Nunez, Samantha Brokenshire, Poyyapakkam Srivaths, Joseph Angelo, Shweta Shah, Mini Michael; Project administration: Samara M. Mendez Nunez, Samantha Brokenshire; Resources: Not applicable; Software: Samara M. Mendez Nunez; Supervision: Samantha Brokenshire, Mini Michael; Validation: Samara M. Mendez Nunez, Samantha Brokenshire; Visualization: Samara M. Mendez Nunez, Samantha Brokenshire; Writing – original draft: Samara M. Mendez Nunez, Samantha Brokenshire; Writing – review \u0026amp; editing: Poyyapakkam Srivaths, Joseph Angelo, Shweta Shah, Mini Michael.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eMichael M, Bagga A, Sartain SE, Smith RJH (2022) Haemolytic uraemic syndrome. Lancet 400(10364):1722-1740. https://doi.org/10.1016/S0140-6736(22)01202-8 \u003c/li\u003e\n\u003cli\u003eLoirat C, Fakhouri F, Ariceta G, Besbas N, Bitzan M, Bjerre A, Coppo R, Emma F, Johnson S, Karpman D, Landau D, Langman CB, Lapeyraque AL, Licht C, Nester C, Pecoraro C, Riedl M, van de Kar NC, Van de Walle J, Vivarelli M, Fr\u0026eacute;meaux-Bacchi V; HUS International (2016) An international consensus approach to the management of atypical hemolytic uremic syndrome in children. 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Pediatr Nephrol 33(3):457-461. https://doi.org/10.1007/s00467-017-3813-2.\u003c/li\u003e\n\u003cli\u003eVolokhina E, Wijnsma K, van der Molen R, Roeleveld N, van der Velden T, Goertz J, Sweep F, Br\u0026uuml;ggemann RJ, Wetzels J, van de Kar N, van den Heuvel L (2017) Eculizumab dosing regimen in atypical hus: possibilities for individualized treatment. Clin Pharmacol Ther 102(4):671-678. https://doi.org/10.1002/cpt.686.\u003c/li\u003e\n\u003cli\u003eGatault P, Brachet G, Ternant D, Degenne D, R\u0026eacute;cipon G, Barbet C, Gyan E, Gouilleux-Gruart V, Bordes C, Farrell A, Halimi JM, Watier H (2015) Therapeutic drug monitoring of eculizumab: Rationale for an individualized dosing schedule. Mabs 7(6):1205-11. https://doi.org/10.1080/19420862.2015.1086049\u003c/li\u003e\n\u003cli\u003eWillrich MAV, Andreguetto BD, Sridharan M, Fervenza FC, Tostrud LJ, Ladwig PM, Rivard AM, Hetrick MD, Olson RN, Bryant SC, Snyder MR, Murray DL (2018) The impact of eculizumab on routine complement assays. J Immunol Methods 460:63-71. https://doi.org/10.1016/j.jim.2018.06.010.\u003c/li\u003e\n\u003cli\u003eWijnsma KL, Duineveld C, Wetzels JFM, van de Kar NCAJ (2019) Eculizumab in atypical hemolytic uremic syndrome: strategies toward restrictive use. Pediatr Nephrol 34(11):2261-2277. https://doi.org/10.1007/s00467-018-4091-3. Erratum in: (2019) Pediatr Nephrol 34(4):741-742. https://doi.org/10.1007/s00467-018-4186-x.\u003c/li\u003e\n\u003cli\u003eSridharan M, Go RS, Willrich MAV (2022) Clinical utility and potential cost savings of pharmacologic monitoring of eculizumab for complement-mediated thrombotic microangiopathy. Mayo Clin Proc Innov Qual Outcomes 6(5):458-464. https://doi.org/10.1016/j.mayocpiqo.2022.03.005. Erratum in: (2024) Mayo Clin Proc Innov Qual Outcomes 11;8(5):480. https://doi.org/10.1016/j.mayocpiqo.2024.06.004.\u003c/li\u003e\n\u003cli\u003eTer Avest M, Langemeijer SMC, Schols SEM, Burger DM, van de Kar NCAJ, Blijlevens NMA, Kievit W, Ter Heine R (2021) The potential of individualized dosing of ravulizumab to improve patient-friendliness of paroxysmal nocturnal haemoglobinuria treatment at reduced costs. Br J Clin Pharmacol 87(8):3359-3363. https://doi.org/10.1111/bcp.14748.\u003c/li\u003e\n\u003cli\u003eCataland S, Ariceta G, Chen P, Dixon B (2019) Discordance between free C5 and CH50 complement assays in measuring complement C5 inhibition in patients with aHUS treated with ravulizumab. Blood\u003cem\u003e \u003c/em\u003e134(Supplement_1):1099. https://doi.org/10.1182/blood-2019-122421\u003c/li\u003e\n\u003cli\u003eSahelijo L, Mujeebuddin A, Mitchell D, Larouche R. First in human single ascending dose study: safety, biomarker, pharmacokinetics and exposure-response relationships of ALXN1210, a humanized monoclonal antibody to C5, with marked half-life extension and potential for significantly longer dosing intervals. In: American Society of Hematology Washington, DC, 2015.\u003c/li\u003e\n\u003cli\u003eWillrich MAV, Ladwig PM, Martinez MA, Sridharan MR, Go RS, Murray DL; Complement Alternative Pathway Thrombotic Microangiopathy (CAP-TMA) Disease Oriented Group at the Mayo Clinic (2021) Monitoring ravulizumab effect on complement assays. J Immunol Methods 490:112944. https://doi.org/10.1016/j.jim.2020.112944.\u003c/li\u003e\n\u003cli\u003eLadwig PM, Barnidge DR, Willrich MA (2017) Quantification of the igg2/4 kappa monoclonal therapeutic eculizumab from serum using isotype specific affinity purification and microflow lc-esi-q-tof mass spectrometry. J Am Soc Mass Spectrom 28(5):811-817. https://doi.org/10.1007/s13361-016-1566-y.\u003c/li\u003e\n\u003cli\u003eTomazos I, Hatswell AJ, Cataland S, Chen P, Freemantle N, Lommele \u0026Aring;, Deighton K, Knowles E, Sheerin NS, Rondeau E (2022) Comparative efficacy of ravulizumab and eculizumab in the treatment of atypical hemolytic uremic syndrome: An indirect comparison using clinical trial data. Clin Nephrol 97(5):261-272. https://doi.org/10.5414/CN110516.\u003c/li\u003e\n\u003cli\u003eFlynn JT, Kaelber DC, Baker-Smith CM, Blowey D, Carroll AE, Daniels SR, de Ferranti SD, Dionne JM, Falkner B, Flinn SK, Gidding SS, Goodwin C, Leu MG, Powers ME, Rea C, Samuels J, Simasek M, Thaker VV, Urbina EM; SUBCOMMITTEE ON SCREENING AND MANAGEMENT OF HIGH BLOOD PRESSURE IN CHILDREN (2017) Clinical practice guideline for screening and management of high blood pressure in children and adolescents. Pediatrics 140(3):e20171904. https://doi.org/10.1542/peds.2017-1904. Erratum in: (2017) Pediatrics 140(6):e20173035. https://doi.org/10.1542/peds.2017-3035. Erratum in: (2018) Pediatrics 142(3):e20181739. https://doi.org/10.1542/peds.2018-1739. PMID: 28827377.\u003c/li\u003e\n\u003cli\u003eTer Avest M, Steenbreker H, Bouwmeester RN, Duineveld C, Wijnsma KL, van den Heuvel LPWJ, Langemeijer SMC, Wetzels JFM, van de Kar NCAJ, Ter Heine R; CUREiHUS Study Group (2023) Proteinuria and exposure to eculizumab in atypical hemolytic uremic syndrome. Clin J Am Soc Nephrol 18(6):759-766. https://doi.org/10.2215/CJN.0000000000000145. \u003c/li\u003e\n\u003cli\u003eBouwmeester RN, Ter Avest M, Wijnsma KL, Duineveld C, Ter Heine R, Volokhina EB, Van Den Heuvel LPWJ, Wetzels JFM, van de Kar NCAJ. (2021) Case report: Variable pharmacokinetic profile of eculizumab in an aHUS patient. Front Immunol 11:612706. https://doi.org/10.3389/fimmu.2020.612706.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"pediatric-nephrology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"pnep","sideBox":"Learn more about [Pediatric Nephrology](http://link.springer.com/journal/467)","snPcode":"467","submissionUrl":"https://www.editorialmanager.com/pnep/default2.aspx","title":"Pediatric Nephrology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Ravulizumab, Complement inhibitor, Pediatrics, Atypical Hemolytic Uremic Syndrome, Pharmacokinetics","lastPublishedDoi":"10.21203/rs.3.rs-7216678/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7216678/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e\u003cp\u003eRavulizumab drug monitoring has not been explored for maintenance therapy in patients with atypical hemolytic uremic syndrome (aHUS). Phase III trials suggest standard dosing regimen provides troughs about 3-fold higher than needed to suppress complement activity. We describe the use of ravulizumab in pediatric patients with aHUS in remission, exploring potential modified dosing strategies based on serum drug level and complement markers.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e\u003cp\u003eThis single-center, retrospective cohort study included pediatric patients with aHUS in remission receiving outpatient ravulizumab infusions between June 30, 2023 and March 31, 2024 with at least one ravulizumab trough. Patients received a standard (SR) or a modified (MR) regimen, determined by the nephrologist. The primary outcome was to describe troughs and corresponding AH50 for patients on at least two equal doses. Secondary outcomes included comparison of troughs by regimen, intra-patient variability, possible adverse drug events (pADE), and drug costs.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003eNine patients were included. The mean ravulizumab trough level was 399.1 (\u0026plusmn;\u0026thinsp;107.3) mcg/mL. All patients exceeded goal of 175 mcg/mL and achieved AH50\u0026thinsp;\u0026lt;\u0026thinsp;10%. Four patients (44%) received ravulizumab according to a MR. No difference was observed in ravulizumab trough levels between SR and MR groups (p\u0026thinsp;=\u0026thinsp;0.67). Patients with multiple troughs showed low intra-patient variability (CV\u0026thinsp;\u0026lt;\u0026thinsp;25%). pADE rates were similar across regimens, and MR was associated with lower drug costs.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e\u003cp\u003eIndividualized maintenance regimens of ravulizumab based on trough and complement monitoring appears safe and effective while reducing drug costs. Further study is needed to define optimal ravulizumab maintenance dosing strategy.\u003c/p\u003e","manuscriptTitle":"Evaluation of Ravulizumab Trough Levels in Pediatric Atypical Hemolytic Uremic Syndrome in Remission","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-05 13:58:01","doi":"10.21203/rs.3.rs-7216678/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major Revisions Needed","date":"2025-09-02T13:40:49+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2025-08-04T21:54:33+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-30T00:36:55+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-29T16:17:29+00:00","index":"","fulltext":""},{"type":"submitted","content":"Pediatric Nephrology","date":"2025-07-25T14:30:30+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"pediatric-nephrology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"pnep","sideBox":"Learn more about [Pediatric Nephrology](http://link.springer.com/journal/467)","snPcode":"467","submissionUrl":"https://www.editorialmanager.com/pnep/default2.aspx","title":"Pediatric Nephrology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"1cbfbc88-1218-47a7-9340-496688f121c4","owner":[],"postedDate":"August 5th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-01-12T16:09:37+00:00","versionOfRecord":{"articleIdentity":"rs-7216678","link":"https://doi.org/10.1007/s00467-025-07113-5","journal":{"identity":"pediatric-nephrology","isVorOnly":false,"title":"Pediatric Nephrology"},"publishedOn":"2026-01-10 15:58:52","publishedOnDateReadable":"January 10th, 2026"},"versionCreatedAt":"2025-08-05 13:58:01","video":"","vorDoi":"10.1007/s00467-025-07113-5","vorDoiUrl":"https://doi.org/10.1007/s00467-025-07113-5","workflowStages":[]},"version":"v1","identity":"rs-7216678","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7216678","identity":"rs-7216678","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}