Population pharmacokinetics of antifibroblast activation protein monoclonal antibody F19 in cancer patients

AIMS: The population pharmacokinetics of 131I-mAbF19, a radiolabelled murine monoclonal antibody against fibroblast activation protein and a potential antitumour stroma agent, were investigated during two phase I studies in cancer patients. METHODS: 131I-mAbF19 serum concentration-time data were obtained in 16 patients from two studies involving imaging and dosimetry in colorectal carcinoma and soft tissue sarcoma. Doses of 0.2, 1 and 2 mg antibody were administered as 60 min intravenous infusions. The data were analysed by nonlinear mixed effect modelling. RESULTS: The data were described by a two-compartment model. Population mean values were 109 ml h(-1) for total serum clearance, 3.1 l for the volume of distribution of the central compartment, and 4.9 l for the volume of distribution at steady state. Mean terminal half-life was 38 h. Intersubject variability was high, but no patient covariates could be identified that further explained this variability. In particular, there was no influence of tumour type or mAbF19 dose. CONCLUSIONS: The pharmacokinetics of antistromal mAbF19 were well defined in these two studies with different solid tumour types, and were comparable with those of other murine monoclonal antibodies that do not bind to normal tissue antigens or blood cells.     

Pharmacokinetics of a Mouse/Human Chimeric Monoclonal Antibody (C-17-1 A) in Metastatic Adenocarcinoma Patients

The pharmacokinetic characteristics of a mouse/human chimeric monoclonal antibody (C-17-1A) were determined in 10 patients with metastatic adenocarcinoma following the administration of either 10-mg or 40-mg infusions as a single or multiple dose. The administration of single 10-mg (n = 5) and 40-mg (n = 5) doses infused over 1 hr resulted in mean apparent steady-state distribution volumes of 4.13 ± 0.97 and 5.16 ± 1.92 liters, respectively, indicating that C-17-1A appears to distribute throughout the vascular compartment and into limited extracellular fluid volume. The disposition of C-17-1A was adequately characterized using a two-compartment open model with mean distribution half-lives of 15.8 and 18.5 hr and mean elimination half-lives of 90.0 and 97.6 hr for the 10- and 40-mg groups, respectively. A linear relationship was observed between AUC and dose (µLg/kg). The clearance of C-17-1A was correlated linearly with total Ig, IgG, and tumor size. Multiple administration of either 10-mg (n = 3) or 40-mg (n = 3) doses of C-17-1A infused over 1 hr every 14 days for a total of three doses resulted in superimposable mean serum concentration versus time data and consistent mean pharmacokinetic characteristics. These data indicate that C-17-1A exhibits linear, nonsaturable distribution and elimination characteristics in man over the dose range studied (i.e., 130 to 880 µg/kg). The multiple-dose pharmacokinetics of C-17-1A were predictable, indicating a lack of an antibody response to C-17-1A over a period of 42 days. The clearance of C-17-1A exhibited large interindividual variability with significant correlations to circulating IgG levels and tumor size.     

肾病综合征患者他克莫司的群体药动学研究

目的 应用非线性混合效应模型NONMEM考察成人肾病综合征患者他克莫司的群体药动学特征。方法 回顾性收集肾病综合征患者51例,246个血药浓度监测数据。以其年龄、性别、体质量、他克莫司日剂量、肝肾功能及合并用药等为协变量,采用具有一级吸收和消除的一室模型拟合数据,并通过自举法和正态化预测分布误差法对模型进行验证。结果 他克莫司的表观清除率（CL/F）为13.9 L·h^-1,表观分布容积（V/F）为382 L,他克莫司日剂量（DD,mg·d^-1）、红细胞压积（HCT）、合并使用五酯胶囊对CL/F有显著影响。模型评价显示该模型及参数估算值可靠稳定,CL/F的最终模型为CL/F=13.9×0.668^WZ×（DD/2）^0.354×（HCT/0.394）^-0.522,其中合并使用五酯胶囊时WZ为1,反之为0。结论 建立的肾病综合征患者口服他克莫司的群体药动学模型能较好地估算患者的群体及个体药动学参数,可为该药的个体化给药方案设计提供参考。     

Rationale for Fixed Dosing of Pertuzumab in Cancer Patients Based on Population Pharmacokinetic Analysis

Objective Our objectives were to develop the population pharmacokinetic (PK) for pertuzumab and examine the variability of steady-state trough serum concentrations (C_SS,trough) and exposure after fixed, body-weight-based, or body-surface area (BSA)-based dosing methods in cancer patients. Methods Pertuzumab was administered by IV infusion (every 3 weeks) either as a weight-based dose (0.5–15 mg/kg) or a fixed dose (420 or 1050 mg). Data from three clinical studies, comprising 153 patients and 1458 concentration-time points, were pooled for this analysis using NONMEM. Results A linear two-compartment model best described the data. Body weight and BSA were significant covariates affecting clearance (CL) and distribution volume (Vc), respectively. However, weight and BSA only explained small percentage of interpatient variability for CL and Vc, respectively. Simulation results indicated that PK profiles were very similar after the three dosing methods. Compared to fixed dosing, weight- and BSA-based dosing only reduced the population variability of C_SS,trough moderately. Conclusion A population PK model was developed for pertuzumab, the first monoclonal IgG1 antibody in a new class of agents known as HER dimerization inhibitors. In addition, our analyses demonstrate the feasibility of administering pertuzumab using a fixed dose in women with ovarian and breast cancers.     

Identification of Sites of Degradation in a Therapeutic Monoclonal Antibody by Peptide Mapping

A peptide mapping procedure was developed to locate regions of a monoclonal antibody, OKT3, that undergo chemical modification as the molecule degrades upon storage. The structures of these peptide degradation products were investigated. Deamidation at specific asparagine residues and oxidation of a cysteine and several methionines were found to be major routes of OKT3 degradation. A unique chain cross-linked degradation product was also observed and characterized. Changing the storage conditions of the antibody affected the relative distribution of degradation products. These results were useful in the development of more stable formulations for OKT3, and the methods can be used in the characterization of other monoclonal antibodies intended for therapeutic use.     

Pharmacokinetics/Pharmacodynamics of Nondepleting Anti-CD4 Monoclonal Antibody (TRX1) in Healthy Human Volunteers

Purpose TRX1 is a nondepleting anti-CD4 monoclonal IgG1 antibody being developed to induce tolerance by blocking CD4-mediated functions. The purpose of this study is to describe the pharmacokinetics (PK) and pharmacodynamics (PD) of TRX1 and to develop a receptor-mediated PK/PD model that characterizes the relationships between serum TRX1 concentration and total and free CD4 expression in healthy male volunteers. Methods Nine subjects from three dosing cohorts in double-blinded, placebo-controlled phase I clinical study was included in the analysis. Serum TRX1 levels were determined using enzyme-linked immunosorbent assay. Blood total and free CD4 receptor levels were determined by using flow cytometric analyses. The receptor-mediated PK/PD model was developed to describe the dynamic interaction of TRX1 binding with CD4 receptors. Results and Conclusions TRX1 displayed nonlinear pharmacokinetic behavior and the CD4 receptors on T cells were saturated and down-modulated following treatment with TRX1. Results from in vitro studies using purified human T cells suggested that CD4-mediated internalization may constitute one pathway by which CD4 is down-modulated and TRX1 is cleared in vivo. The developed receptor-mediated PK/PD model adequately described the data. This PK/PD model was used to simulate PK/PD time profiles after different dosing regimens to help guide the dose selection in future clinical studies.     

我国已上市治疗用单抗类产品分析

目的：分析我国已上市治疗用单抗类产品存在的差距,明确努力方向。方法：基于我国已上市治疗用单抗类产品批准数据进行统计分析和对比分析。结果：对我国单抗类药物的发展历程、上市时间、批准品种以及我国已批准上市的单抗类药物与FDA单抗类药物的批准情况进行了对比梳理。结论：单抗类药物在生物技术制药中占有重要地位,并逐渐成为生物医药领域发展的主要方向。我国单抗类药物中国产品种与进口品种存在差距,整体上与FDA存在差距。但随着近年来的改革,发展潜力及势头良好。     

Population Pharmacokinetics of Rilotumumab,a Fully Human Monoclonal Antibody Against Hepatocyte Growth Factor,in Cancer Patients

Rilotumumab is an investigational, fully human, monoclonal antibody immunoglobulin G2 against hepatocyte growth factor (HGF) that blocks the binding of HGF to its receptor MET and has shown trends toward improved survival in a phase 2 clinical trial in gastric cancer. To characterize rilotumumab pharmacokinetics in patients with cancer and to identify factors affecting the pharmacokinetics, rilotumumab concentration data from seven clinical trials were analyzed with a nonlinear mixed-effect model. We found that rilotumumab exhibited linear and time-invariant kinetics over a dose range of 0.5–20 mg/kg. Typical systemic clearance and central volume of distribution were 0.184 L/day and 3.56 L, respectively. Body weight is the most significant covariate, and sex, cancer type, coadministration of chemotherapeutics, baseline plasma HGF and tumor MET levels, and renal and hepatic functions did not have an effect on rilotumumab pharmacokinetics. The concentration–time profiles for the rilotumumab clinical regimens were projected well with the model. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 103:328–336, 2014     

Population Pharmacokinetics of Terfenadine

Purpose. After oral administration of terfenadine, plasma concentrations of the parent drug are usually below the limits of quantitation of conventional analytical methods because of extensive first-pass metabolism. Data are usually reported on the carboxylic acid metabolite (Ml) but there are no published reports of pharmacokinetic parameters for terfenadine itself. The present study was undertaken to evaluate the population pharmacokinetics of terfenadine. Methods. Data from 132 healthy male subjects who participated in several different studies were included in this analysis. After an overnight fast, each subject received a single 120 mg oral dose of terfenadine; blood samples were collected for 72 hours. Terfenadine plasma concentrations were measured using HPLC with mass spectrometry detection and Ml plasma concentrations were measured using HPLC with fluorescence detection. A 2-compartment model was fitted to the terfenadine data using NONMEM; terfenadine and Ml data were also analyzed by noncompartmental methods. Results. Population mean Ka was 2.80 hr^–1, T_lag was 0.33 hr, Cl/F was 4.42 × 10³ 1/hr, V_C/F was 89.8 ×10³1, Q/F was 1.85 ×10³ 1/hr and V_p/F was 29.1 × 10³1. Intersubject CV ranged from 66 to 244% and the residual intrasubject CV was 21%. Based on noncompartmental methods, mean terfenadine C_max was 1.54 ng/ml, T_max was 1.3 hr, t_{1/2 Z} was 15.1 hr, Cl/F was 5.48 × 10³ 1/hr and V_z/F was 119.2 × 10³1. Ml concentrations exceeded terfenadine concentrations by more than 100 fold and showed less intersubject variability. Conclusions. Terfenadine disposition was characterized by a 2-compartment model with large intersubject variability, consistent with its significant first-pass effect.     

用NONMEM法建立癫痫患者丙戊酸群体药代动力学模型

目的 建立丙戊酸(VPA)在癫痫患者中的群体药代动力学(PPK)模型,考察固定效应因素对VPA清除率(CL/F)的影响.方法 回顾性收集贵州省人民医院111名癫痫患者VPA稳态血药浓度数据及相应的人口学、合并用药及CYP2A6基因型等资料,随机将患者分成建模组(74名)及验证组(37名),使用建模组数据通过非线性混合效应模型(NONMEM)程序建立VPA的PPK模型.使用验证组数据来验证模型的准确度和精密度,比较基础模型和最终模型的平均预测误差(MPE)、平均绝对误差(MAE)、平均根方差(RMSE).结果 建立的最终模型包含了日用药剂量(DDO)及CYP2A6基因型,模型方程为:CL/F=0.363·DD00.525·1.29GENECYP2A6.最终模型有更好的精密度及准确度,基础模型MPE、MAE、RMSE值为- 10.63、14.40、22.55,最终模型相应值为-6.11、9.06、14.17.结论 本研究初步建立癫痫患者VPA的PPK模型,VPA清除率随日给药剂量的增大而增大,CYP2A6野生型(CYP2A6*1/*1)组患者较CYP2A6突变型(CYP2A6* 1/*4、CYP2A6* 4/*4)组患者有更高的VPA清除率.     

用NONMEM法建立癫痫患者丙戊酸群体药代动力学模型

目的建立丙戊酸（VPA）在癫痫患者中的群体药代动力学（PPK）模型,考察固定效应因素对VPA清除率（CL/F）的影响。方法回顾性收集贵州省人民医院111名癫痫患者VPA稳态血药浓度数据及相应的人口学、合并用药及CYP2A6基因型等资料,随机将患者分成建模组（74名）及验证组（37名）,使用建模组数据通过非线性混合效应模型（NONMEM）程序建立VPA的PPK模型。使用验证组数据来验证模型的准确度和精密度,比较基础模型和最终模型的平均预测误差（MPE）、平均绝对误差（MAE）、平均根方差（RMSE）。结果建立的最终模型包含了日用药剂量（DDO）及CYP2A6基因型,模型方程为：CL/F=0.363.DDO0.525.1.29GENECYP2A6。最终模型有更好的精密度及准确度,基础模型MPE、MAE、RMSE值为-10.631、4.40、22.55,最终模型相应值为-6.11、9.06、14.17。结论本研究初步建立癫痫患者VPA的PPK模型,VPA清除率随日给药剂量的增大而增大,CYP2A6野生型（CYP2A6＊1/＊1）组患者较CYP2A6突变型（CYP2A6＊1/＊4、CYP2A6＊4/＊4）组患者有更高的VPA清除率。     

国人老年患者靶控输注丙泊酚的群体药代动力学

目的研究丙泊酚靶控输注用于国人老年患者的群体药代动力学。方法32例择期下腹部开腹手术的患者,ASAⅠ-Ⅱ级,年龄65～82岁的老年患者,采用靶控输注方式(以血浆浓度为靶)输注丙泊酚,丙泊酚血浆浓度为3μg·mL-1。术中取桡动脉血,以反向高效液相色谱—荧光法测定丙泊酚的血浆浓度。用NONMEM软件分析丙泊酚的药代动力学参数。结果国人老年患者靶控输注丙泊酚的药代动力学过程符合三室开放模型,年龄、瘦体重对中央室清除率有影响,性别对第三分布容积有影响。结论年龄、瘦体重、性别对国人老年患者丙泊酚的药代动力学参数有影响。群体药代动力学参数应用于个体时,应根据个体情况相应调整靶控输注的药代动力学参数,以改善靶控输注系统的精确性。     

Population Pharmacokinetics and Pharmacodynamics of Sotalol in Pediatric Patients with Supraventricular or Ventricular Tachyarrhythmia

Aims: To derive useful pharmacokinetic (PK) and pharmacodynamic (PD) information for guiding the clinical use of sotalol in pediatric patients with supraventricular (SVT) or ventricular tachyarrhythmia (VT).Methods: Two studies were conducted in-patients with SVT or VT in the age range between birth and 12 years old. Both studies used an extemporaneously compounded formulation prepared from sotalol HCl tablets. In the PK study, following a single dose of 30 mg/m² sotalol, extensive blood samples (n=10) were taken. The PK–PD study used a dose escalation design with doses of 10, 30, and 70 mg/m², each administered three times at 8-hr intervals without a washout. Six ECG recordings for determination of QT and RR were obtained prior to the initial dose of sotalol. Four blood samples were collected six ECG's were determined during the third interval at each dose level. Plasma concentrations of sotalol (C) were assayed by LC/MS/MS. The data analysis used NONMEM to obtain the population PK and PD parameter estimates. The individual PK and PD parameters were estimated with empirical Bayes methodology.Results: A total of 611 C from 58 patients, 477 QTc and 499 RR measurements from 23 and 22 patients, respectively, were available for analysis. The PK of sotalol was best described by a linear two-compartment model. Oral clearance (CL/F) and volume of central compartment (Vc/F) were linearly correlated with body surface area (BSA), body weight or age. CL/F was also linearly correlated with creatinine clearance. The best predictor for both CL/F and Vc/F was BSA. The remaining intersubject coefficients of variation (CV's) in CL/F, and Vc/F were 21.6% and 20.3%, respectively. The relationship of QTc to C was adequately described by a linear model. The intersubject CV's in slope (SL) and intercept (E0) were 56.2 and 4.7%, respectively. The relationship of RR to C was also adequately described by a linear model in which the baseline RR and SL were related to age or BSA. The intersubject CV's for SL and E₀ were 86.7 and 14.4%, respectively.Conclusions: BSA is the best predictor for the PK of sotalol. Both QTc and RR effects are linearly related to C. No covariates are found for the QTc–C relation, while the RR–C relation shows age or BSA dependency.     

Inherent Correlation Between Dose and Clearance in Therapeutic Drug Monitoring Settings: Possible Misinterpretation in Population Pharmacokinetic Analyses

During the course of therapeutic drug monitoring (TDM), doses are adjusted to attain a target concentration range and a correlation between clearance (CL) and dose is introduced. In population pharmacokinetic analyses of such TDM data, CL has frequently been modeled as a function of dose. This paper demonstrates by simulation methodology that the TDM process does indeed introduce a correlation between dose and CL which can be interpreted as a nonlinearity. Using literature values of carbamazepine pharmacokinetics, three steady-state concentrations were simulated following a standard 1000 mg total daily dose (TDD) regimen in 100 in silico subjects. A set of clinical rules was established to adjust the TDD based on these three concentrations, as might be done in the clinical setting. Another set of concentrations using these TDM-derived TDDs for each subject (600–1600 mg) was simulated. A standard population pharmacokinetic analysis of the post-TDM data was conducted using NONMEM. This process was replicated 100 times to estimate the type II error rate. When CL was modeled without TDD, plots of WRES versus PRED demonstrated a clear pattern, as did the delta plots of CL (CL minus TVCL) versus TDD, suggesting the covariate TDD should be incorporated into the model. After TDD was included in the model for CL, the objective function value decreased by an average of 75.7 (p < 0.001). In addition, the inter-individual variability in CL expressed as a coefficient of variation decreased by an average of 9.9% and the diagnostic plots improved. Although CL was simulated to be independent of TDD, it was identified as an important covariate using standard approaches in a simulated TDM setting in 100% of the replicated simulation studies. The TDM process introduces a correlation between CL and TDD that can be misinterpreted as nonlinearity in the system     

Protein Structural Conformation and Not Second Virial Coefficient Relates to Long-Term Irreversible Aggregation of a Monoclonal Antibody and Ovalbumin in Solution

Purpose The purpose of the study was to investigate the relationship of the second virial coefficient, B₂₂, to the extent of irreversible protein aggregation upon storage. Methods A monoclonal antibody and ovalbumin were incubated at 37°C (3 months) under various solution conditions to monitor the extent of aggregation. The B₂₂ values of these proteins were determined under similar solution conditions by a modified method of flow-mode static light scattering. The conformation of these proteins was studied using circular dichroism (CD) spectroscopy and second-derivative Fourier transform infrared spectroscopy. Results Both proteins readily aggregated at pH 4.0 (no aggregation observed at pH 7.4); the extent of aggregation varied with the ionic strength and the presence of cosolutes (sucrose, glycine, and Tween 80). Debye plots of the monoclonal antibody showed moderate attractive interactions at pH 7.4, whereas, at pH 4.0, nonlinear plots were obtained, indicating self-association. CD studies showed partially unfolded structure of antibody at pH 4.0 compared with that at pH 7.4. In the case of ovalbumin, similar B₂₂ values were obtained in all solution conditions irrespective of whether the protein aggregated or not. CD studies of ovalbumin indicated the presence of a fraction of completely unfolded as well as partially unfolded species at pH 4.0 compared with that at pH 7.4. Conclusions The formation of a structurally altered state is a must for irreversible aggregation to proceed. Because this aggregation-prone species could be an unfolded species present in a small fraction compared with that of the native state or it could be a partially unfolded state whose net interactions are not significantly different compared with those of the native state, yet the structural changes are sufficient to lead to long-term aggregation, it is unlikely that B₂₂ will correlate with long-term aggregation.     

术中植入缓释氟尿嘧啶在直肠癌患者中的群体药动学研究

目的:建立并考察直肠癌患者术中植入氟尿嘧啶的群体药动学（PPK）模型,为直肠癌患者的临床用药提供个体化指导。方法:通过完整的药动学（PK）采样法收集20名直肠癌患者的血药浓度120个。一室模型为基础,通过使用非线性效应模型拟合法（NONMEM）建立群体药动学模型,考察固定效应（身高、体质量、年龄、性别、肝肾功能、联合用药等）对氟尿嘧啶PK参数的影响。结果:氟尿嘧啶植入剂PPK参数为:Ke（0.005 44±0.002 89）h^-1,Ka（0.748±0.602）h^-1,V/F（1.06±0.343）L·kg^-1,Ke（0.005 7±0.541）h^-1,CL/F（262±0.194）L·kg^-1。模拟1 000个受试者的数据,结果显示血药浓度的90%可信区间基本涵盖实测值,证实了模拟结果的可靠性。结论:本研究成功建立氟尿嘧啶植入剂的群体药动学模型,可以估算个体药动学参数预测血药浓度,满足优化个体化给药的需要。     

Structural Characterization of a Recombinant Monoclonal Antibody by Electrospray Time-of-Flight Mass Spectrometry

Purpose The aim of this study was to perform structural characterization of a recombinant monoclonal antibody (MAb), huN901, by electrospray time-of-flight mass spectrometry (ESI-TOFMS) using both “top-down” and “bottom-up” approaches.Methods In the top-down approach, the molecular masses of the deglycosylated huN901 and the light and heavy chains of the antibody were measured by direct infusion MS and liquid chromatography–mass spectrometry (LC–MS). In the bottom-up approach, trypsin and Asp-N protease were used to digest the separated, reduced and alkylated light and heavy chains followed by LC–MS analysis of the digests.Results The primary structure and post-translational modifications of huN901 were characterized by both top-down and bottom-up MS approaches. Modifications of N-terminal pyroglutamate formation, cleavage of C-terminal lysine, glycosylation, and deamidation were identified in the antibody heavy chain by both protein mass measurement and peptide mapping. No modifications were found in the complementarity determining regions (CDRs) of both chains. Both trypsin and Asp-N protease digestion had an average sequence recovery of 97%, and generated complimentary mapping results with complete sequence recovery.Conclusions ESI-TOFMS is a superior tool to characterize MAb and other complex protein pharmaceuticals.     

Population Pharmacokinetics of Risperidone and 9-Hydroxyrisperidone in Patients with Acute Episodes Associated with Bipolar I Disorder

A population model was developed with the aim to simultaneously describe risperidone and 9-hydroxyrisperidone pharmacokinetics; to obtain estimates for pharmacokinetic parameters and associated inter- and intra-individual variability of risperidone and 9-hydroxyrisperidone; and to evaluate the influence of patient demographic characteristics and other factors on risperidone, 9-hydroxyrisperidone, and active moiety pharmacokinetics. Data were obtained from 407 patients enrolled in four Phase 1 (serial blood sampling) and three Phase 3 trials (sparse sampling), representing dosage regimens ranging from 4 mg single dose to flexible 1–6 mg once daily. A pharmacokinetic model with two-compartment submodels for risperidone and 9-hydroxyrisperidone disposition and a sequential zero- and first-order absorption pathway was selected based on prior knowledge. A mixture model was incorporated due to CYP2D6 polymorphism of risperidone conversion to 9-hydroxyrisperidone. Patient characteristics tested as potential covariates were: age, sex, race, body weight, lean body mass, body mass index, creatinine clearance, liver function laboratory parameters, study, and carbamazepine comedication. The quasi-clearance of active moiety (the sum of risperidone and 9-hydroxyrisperidone) was simulated and linear regression performed to identify significant covariates. The selected pharmacokinetic model described the plasma concentration-time profiles for risperidone and 9-hydroxyrisperidone quite well and was able to determine each patient’s phenotype. Covariates significantly affecting the pharmacokinetics were carbamazepine comedication, and study because the proportion of patients assigned to the intermediate metabolizer status decreased from single to multiple dosing while the proportion assigned to extensive metabolizer status increased. Covariates with limited and clinically irrelevant effects on active moiety concentrations were patient phenotype, race, and total protein. Carbamazepine also decreased active moiety concentrations.     

Population Pharmacokinetics of Baloxavir Marboxil in Japanese Pediatric Influenza Patients

Baloxavir marboxil is a prodrug of baloxavir acid, an inhibitor of cap-dependent endonuclease, and suppresses the replication of influenza virus. The aim of this study was to investigate its pharmacokinetic characteristics in Japanese pediatrics. Population pharmacokinetic analysis was conducted for baloxavir acid with 328 plasma concentration data points in a clinical study of 107 Japanese pediatric influenza patients. The plasma baloxavir acid concentration profiles were well captured by a 2-compartment model including first-order absorption and lag time. Body weight was considered to be the most crucial covariate, which affects clearance and volume of distribution. The body weight–based dose regimen (10 mg for 10 kg to less than 20 kg pediatrics, 20 mg for 20 kg to less than 40 kg pediatrics, and 40 mg for at least 40 kg pediatrics) for Japanese pediatrics can provide comparable exposure to baloxavir acid to that for adults. In conclusion, the population pharmacokinetic model would be useful to comprehend the characteristics of baloxavir acid pharmacokinetics in pediatric patients.