Pharmacokinetic/Pharmacodynamic Modellingof GnRH Antagonist Degarelix: A Comparisonof the Non-linear Mixed-Effects Programs NONMEM and NLME

In this paper, the two non-linear mixed-effects programs NONMEM and NLME were compared for their use in population pharmacokinetic/pharmacodynamic (PK/PD) modelling. We have described the first-order conditional estimation (FOCE) method as implemented in NONMEM and the alternating algorithm in NLME proposed by Lindstrom and Bates. The two programs were tested using clinical PK/PD data of a new gonadotropin-releasing hormone (GnRH) antagonist degarelix currently being developed for prostate cancer treatment. The pharmacokinetics of intravenous administered degarelix was analysed using a three compartment model while the pharmacodynamics was analysed using a turnover model with a pool compartment. The results indicated that the two algorithms produce consistent parameter estimates. The bias and precision of the two algorithms were further investigated using a parametric bootstrap procedure which showed that NONMEM produced more accurate results than NLME together with the nlmeODE package for this specific study.     

Use of a Target‐Mediated Drug Disposition Model to Predict the Human Pharmacokinetics and Target Occupancy of GC1118, an Anti‐epidermal Growth Factor Receptor Antibody

GC1118 is an anti‐epidermal growth factor receptor (EGFR) monoclonal antibody that is currently under clinical development. In this study, the pharmacokinetics (PK) of GC1118 were modelled in monkeys to predict human PK and receptor occupancy (RO) profiles. The serum concentrations of GC1118 and its comparator (cetuximab) were assessed in monkeys with a non‐compartmental analysis and a target‐mediated drug disposition (TMDD) model after intravenous infusion (3–25 mg/kg) of these drugs. The scaling exponent of the EGFR synthesis rate was determined using a sensitivity analysis. The human cetuximab exposures were simulated by applying different exponents (0.7–1.0) for the EGFR synthesis rate in the allometric monkey PK model. Simulated C_max and area under the curve values therein were compared with those previously reported in the literature to find the best exponent for the EGFR synthesis rate in human beings. The TMDD model appropriately described the monkey PK profile, which showed a decrease in clearance (CL; 1.2–0.4 ml/hr/kg) as the dose increased. The exponents for CL (0.75) and volume of distribution (Vd; 1.0) were used for the allometric scaling to predict human PK. The allometric coefficient for the EGFR synthesis rate chosen by the sensitivity analysis was 0.85, and the RO profiles that could not be measured experimentally were estimated based on the predicted concentrations of the total target and the drug–target complex. Our monkey TMDD model successfully predicts human PK and RO profiles of GC1118 and can be used to determine the appropriate dose for a first‐in‐human study investigating this drug.     

Non-linear mixed effect modeling of the time-variant disposition of erythropoietin in anemic cancer patients

Chemotherapy‐induced anemia is a frequent complication in cancer treatment. The aim was to develop a pharmacokinetic (PK) model that describes the time‐dependent decline of epoetin alfa (rHuEPO) clearance following thrice (t.i.w.) or once (q.w.) weekly subcutaneous injections in cancer patients using a population PK approach. Serum concentrations of rHuEPO were available retrospectively from a phase I study. A one‐compartment model with first‐order elimination described rHuEPO PK. Sequential zero‐ and first‐order (k_a) processes with duration (t_lag) characterized the absorption. Population PK analysis was performed using NONMEM. The influence of several covariates was tested. Model evaluation was performed using visual predictive check. Precision of parameter estimates was assessed by standard errors and confidence intervals determined by bootstrap analysis. Apparent clearance (CL/F) and volume of distribution (V_c/F) were 25.6% lower and 29.2% higher for q.w. than t.i.w. groups. RHuEPO was absorbed for 10% during 24.6 h through the zero‐order process. Following which 90% of the dose was absorbed through the first‐order process with k_a of 0.033 h^?1. The most significant covariates were the time‐dependent decrease of CL/F with an increase in body weight, a decrease in reticulocyte count, a decrease in hemoglobin baseline, an increase in total number of chemotherapy cycles, and platinum‐containing chemotherapy. AGE served as an important covariate on FRAC and k_a. Visual predictive check showed no deviation from observed values. The PK model adequately predicted rHuEPO concentration‐profiles in all individuals. Relevant covariates were identified and incorporated into the model. Copyright © 2010 John Wiley & Sons, Ltd.     

Population Pharmacokinetic–Pharmacogenetic Model of Tacrolimus in the Early Period after Kidney Transplantation

As tacrolimus has a rather narrow therapeutic range and high individual variability in its pharmacokinetics, it is important to determine the cause of the variation in tacrolimus pharmacokinetics. The purpose of this study was to establish a population pharmacokinetic–pharmacogenetic model of tacrolimus and identify covariates that affect pharmacokinetic parameters to prevent fluctuations in the tacrolimus trough concentration during the early period after transplantation. Data from 1501 trough concentrations and 417 densely collected concentrations were compiled from 122 patients who were on post‐operative days 10–20 and analysed with a nonlinear mixed‐effect model. The first‐order conditional estimation (FOCE) with interaction method was used to fit the model using the NONMEM program. Clinical/laboratory data were also collected for the same period, and CYP3A5 and ABCB1 genotypes were analysed for use in modelling from all included patients. An empirical Bayesian approach was used to estimate individual pharmacokinetic profiles. A one‐compartment model with first absorption and elimination and lag time best described the data. The estimated population mean of clearance (CL/F), volume of distribution (V/F) and absorption rate (K_a) were 21.9 L/hr, 205 L, and 3.43/hr, respectively, and the lag time was fixed at 0.25 hr. Clearance increased with days after transplantation and decreased with CYP3A5*3/*3 about 18.4% compared with CYP3A5*1 carriers (p < 0.001). A population pharmacokinetic model was developed for tacrolimus in early post‐kidney transplantation recipients to identify covariates that affect tacrolimus pharmacokinetics. Post‐operative days and CYP3A5 genotype were confirmed as critical factors of tacrolimus pharmacokinetics.     

A Simple Dosing Scheme for Intravenous Busulfan Based on Retrospective Population Pharmacokinetic Analysis in Korean Patients

Busulfan is an antineoplastic agent with a narrow therapeutic window. A post-hoc population pharmacokinetic analysis of a prospective randomized trial for comparison of four-times daily versus once-daily intravenous busulfan was carried out to search for predictive factors of intravenous busulfan (iBu) pharmacokinetics (PK). In this study the population PK of iBu was characterized to provide suitable dosing recommendations. Patients were randomized to receive iBu, either as 0.8 mg/kg every 6 h or 3.2 mg/kg daily over 4 days prior to hematopoietic stem cell transplantation. In total, 295 busulfan concentrations were analyzed with NONMEM. Actual body weight and sex were significant covariates affecting the PK of iBu. Sixty patients were included in the study (all Korean; 23 women, 37 men; mean [SD] age, 36.5 [10.9] years; weight, 66.5 [11.3] kg). Population estimates for a typical patient weighing 65 kg were: clearance (CL) 7.6 l/h and volume of distribution (V_d) 32.2 l for men and 29.1 L for women. Inter-individual random variabilities of CL and V_d were 16% and 9%. Based on a CL estimate from the final PK model, a simple dosage scheme to achieve the target AUC_0-inf (defined as median AUC_0-inf with a once-daily dosage) of 26.18 mg/l·hr, was proposed: 24.79·ABW^0.5 mg q24h, where ABW represents the actual body weight in kilograms. The dosing scheme reduced the unexplained interindividual variabilities of CL and Vd of iBu with ABW being a significant covariate affecting clearance of iBU. We propose a new simple dosing scheme for iBu based only on ABW.     

Evidence of Different Propofol Pharmacokinetics under Short and Prolonged Infusion Times in Rabbits

Propofol is an anaesthetic widely used in both human beings and animals. However, the characterization of propofol pharmacokinetics (PK) is not well understood when long‐term infusions are used. The main objective of this study was to explore the PK behaviour of propofol in a rabbit model during short and prolonged propofol infusions and to develop an internally validated PK model, for propofol dose individualization in the rabbit for future use. Population 1 (P1) was constituted by seven New Zealand rabbits and was used to characterize the PK profile of propofol at short infusions. Animals were anaesthetized with a bolus of 20 mg/kg, followed by an infusion rate of 50 mg/kg/hr of propofol at 1%, which was then maintained for 30 min. A second rabbit population (P2, n = 7) was sedated according to reflexes responses and Index of Consciousness values, for 20 consecutive hours using propofol 2% aiming at characterizing propofol behaviour at long‐term infusions. Clinical data and blood samples were collected at specific time‐points in both populations. Propofol plasma concentrations were determined by gas chromatography/ion trap mass spectrometry. The NONMEM VII software was used to evaluate the relationships between dose and plasma concentrations. A linear two‐compartment model with different central compartment volume and plasma clearance (separately modelled in the two populations) was the one that best described propofol concentrations. The time course of propofol plasma concentrations was well characterized by the PK model developed, which simultaneously accounts for propofol short‐ and long‐term infusions and can be used to optimize future PK studies in rabbits.     

Prediction of the tacrolimus population pharmacokinetic parameters according to CYP3A5 genotype and clinical factors using NONMEM in adult kidney transplant recipients

Purpose

Tacrolimus is a commonly used immunosuppressant in solid organ transplantation recipients, but it is characterized by a narrow therapeutic range and large inter-individual variability. The purpose of this study was to establish a population pharmacokinetic (PK) model of tacrolimus and evaluate the influence of clinical covariates, including the genetic polymorphisms of the cytochrome P450 3A5 gene (CYP3A5) and gene encoding P-glycoprotein (ABCB1), on the PK parameters in adult Korean kidney transplant recipients.

Methods

Clinical data were collected retrospectively for 400 days after the initiation of a tacrolimus-based immunosuppression therapy. Data from 2,788 trough blood samples obtained from 80 subjects were used to perform a population PK analysis with a nonlinear mixed-effect model (NONMEM).

Results

The estimated population mean values of clearance (CL/F) and volume of distribution (V/F) were 22.9 L/h and 716 L, respectively, and the k _a was fixed to 4.5 h^-1. The CYP3A5 genotype, hematocrit level, and post-operative days were identified as the main covariates that influence CL/F, and body weight was found to have a significant effect on V/F. Other covariates, including ABCB1 genotype, corticosteroid dosage, sex, and other clinical data, did not contribute to the pharmacokinetics of tacrolimus.

Conclusions

This tacrolimus population PK model will be a valuable tool in developing rational guidelines and provides a basis for individualized therapy after kidney transplantation in clinical settings of Korea.     

Mixed-effects modelling of the interspecies pharmacokinetic scaling of pegylated human erythropoietin

The aim of this study was to develop a population pharmacokinetic model for interspecies allometric scaling of pegylated r-HuEPO (PEG-EPO) pharmacokinetics to man. A total of 927 serum concentrations from 193 rats, 6 rabbits, 34 monkeys, and 9 dogs obtained after a single dose of PEG-EPO, administered by the i.v. (dose range: 12.5–550 μg/kg) and s.c. (dose range: 12.5–500 μg/kg) routes, were pooled in this analysis. An open two-compartment model with first-order absorption and lag time (Tlag) and linear elimination from the central compartment was fitted to the data using the NONMEM V software. Body weight (WT) was used as a scaling factor and the effect of brain weight (BW), sex, and pregnancy status on the pharmacokinetic parameters was investigated. The final model was evaluated by means of a non-parametric bootstrap analysis and used to predict the PEG-EPO pharmacokinetic parameters in healthy male subjects. The systemic clearance (CL) in males was estimated to be 4.08WT1.030 × BW−0.345 ml/h. In females, the CL was 90.7% of the CL in males. The volumes of the central (Vc) and the peripheral (Vp) compartment were characterized as 57.8WT0.959 ml, and 48.1WT1.150 ml, respectively. Intercompartmental flow was estimated at 2.32WT0.930 ml/h. Absorption rate constant (Ka) was estimated at 0.0538WT−0.149. The absolute s.c. bioavailability F was calculated at 52.5, 80.2, and 49.4% in rat, monkey, and dog, respectively. The interindividual variability in the population pharmacokinetic parameters was fairly low (<35%). Non-parametric bootstrap confirmed the accuracy of the NONMEM estimates. The mean model predicted pharmacokinetic parameters in healthy male subjects of 70 kg were estimated at: CL: 26.2 ml/h; Vc: 3.6 l; Q: 286 l/h; Vp: 6.9 l, and Ka: 0.031 h⁻¹. The population pharmacokinetic model developed was appropriate to describe the time course of PEG-EPO serum concentrations and their variability in different species. The model predicted pharmacokinetics of PEG-EPO in humans suggest a less frequent dosing regimen relative to erythropoietin and darbepoetin, potentially leading to a simplification of anemia management.     

Quantitative Assessment of Food Effect on the Pharmacokinetics of Nano‐Crystallized Megestrol Acetate

Megestrol acetate, an appetite stimulant with low bioavailability, shows increased bioavailability when taken together with food. However, the pharmacokinetic characteristics of megestrol acetate and its relation with food are not well understood. This study aimed to investigate the food effect on the pharmacokinetics (PK) of the recently developed nano‐crystallized megestrol acetate (NCMA), using a model‐based approach. Data were obtained from an NCMA PK study consisting of a single dose in fasting (39 individuals) and fed conditions (40 individuals). Plasma concentrations were measured up to 120 hr after dosing. With the incorporation of body‐weight via allometry, NONMEM 7.3 was used to develop a PK model, which was then used to simulate an optimal fasting dose yielding an area under concentration (AUC) and maximum concentration (C_max) of NCMA close to those obtained with the fed dose. NCMA concentrations were best characterized by a two‐compartment model with first‐order absorption linked to a recycling compartment to account for the multiple concentration peaks observed. Food increased bioavailability 2.2 times and decreased the absorption rate constant 0.58 times. Recycling event times were estimated to be 3.56, 7.99 and 24.0 hr. The optimal fast dose was 2.0 times higher than the fed dose, and the resulting difference in drug exposure between the fasting and fed dose was 7.5%. This work suggests that the PK model developed can be applied to an optimal dosage regimen design for NCMA treatment.     

Population Pharmacokinetic Meta‐Analysis of Vortioxetine in Healthy Individuals

The objective was to describe the pharmacokinetics of vortioxetine and evaluate the effect of intrinsic and extrinsic factors in the healthy population. Data from 26 clinical pharmacology studies were pooled. A total of 21,758 vortioxetine quantifiable plasma concentrations were collected from 887 subjects with corresponding demography. The doses ranged from 2.5 to 75 mg (single dose) and 2.5–60 mg (multiple QD doses). The pharmacokinetics of vortioxetine was best characterised by a two‐compartment model with first‐order absorption, lag‐time and linear elimination, with interindividual error terms for absorption rate constant, oral clearance and central volume of distribution. The population mean was 32.7 L/hr for oral clearance and 1.97?10³ L for the central volume of distribution. The average elimination half‐life was 65.8 hr. CYP2D6 inferred metabolic status (ultra, extensive, intermediate or poor metabolisers) and age on oral clearance and height on central volume of distribution were identified as statistically significant covariate–parameter relationships. For CYP2D6 poor metabolisers, CL/F was approximately 50% to that seen in CYP2D6 extensive metabolisers. The impact of height on V2/F and age on CL/F was low and not considered to be clinically relevant. The final model was found to be reliable, stable and predictive. A reliable, stable and predictive pharmacokinetic model was developed to characterise pharmacokinetics of vortioxetine in the healthy population.     

Evaluation of Bayesian estimation in comparison to NONMEM for population pharmacokinetic data analysis: application to pefloxacin in intensive care unit patients.

The pharmacokinetics of pefloxacin (PF) were investigated in a population of 74 intensive care unit patients receiving 400 mg bid as 1-hr infusion using (i) Bayesian estimation (BE) of individual patient parameters followed by multiple linear regression (MLR) analysis and (ii) NONMEM analysis. The data consisted of 3 to 9 PF plasma levels per patient measured over 1 to 3 dosage intervals (total 113) according to four different limited (suboptimal) sampling 3-point protocols. Twenty-nine covariates (including 15 comedications) were considered to explain the interpatient variability. Predicted PF CL for a patient with median covariates values was similar in both BE/MLR and NONMEM analysis (4.02 and 3.92 L/hr, respectively). Bilirubin level and age were identified as the major determinants of PF CL by both approaches with similar predicted magnitude of effects (about 40 and 30% decrease of median CL, respectively). Confounding effects were observed between creatinine clearance (26% decrease of PF CL in the BE/MLR model), simplified acute physiology score (a global score based on 14 biological and clinical variables) (18% decrease of median CL in the NONMEM model) and age (entered in both models) which were highly correlated in our data base. However, both models predicted similar PF CL for actual subpopulations by using actual covariate values. Finally, the NONMEM analysis allowed identification of an effect of weight on CL (decrease of CL for weight < 65 kg) whereas the BE/MLR analysis predicted an increase of CL in patients treated with phenobarbital. In conclusion, both approaches allowed identification of the major risk factors of PF pharmacokinetics in ICU patients. Their potential use at different stages of drug development is discussed.     

丙戊酸钠在癫痫患者中的群体药动学

目的建立丙戊酸钠在癫痫患者治疗中的群体药动学模型,为临床个体化给药提供参考。方法收集我院门诊60名癫痫患者丙戊酸钠稳态血药浓度监测数据和相应的人口学数据,应用非线性混合效应模型(non linearm ixed-effectmodel,NONMEM)程序对收集的数据进行分析,建立群体药动学模型。结果建立了癫痫患者口服丙戊酸钠群体药代动力学模型:CL/F=0.959×1.04x,(x=0,1),V/F=1.35,ka=2.38 h-1,说明丙戊酸的清除率与患者性别相关,即男性患者的清除率大于女性。结论初步建立癫痫患者口服丙戊酸钠群体药动学模型,为丙戊酸钠个体化用药提供理论基础。     

An Application of the Population Approach to Animal Pharmacokinetics During Drug Development

Abstract

Serum concentrations of a drug under development were obtained from an animal pharmacokinetic study using the one sample per animal design, and analyzed using the population data analysis program, NONMEM. A two compartment open model with IV administration was fitted to the data. Although sex and weight were not predictors of clearance (CL), sex helped to explain the variability in the volume of central compartment (V₁). the variability in CL and V₁ were 23.5 and 23.2%, respectively, while the variability in the transfer rate constants, k₁₂ and k₂₁ were infinitesimal. Removal of variability in these micro rate constants did not affect the NONMEM objective function. the inter-animal variability estimated in these parameters were actually a composite of inter-animal variability and residual intra-animal variability since there was no information in the data sets for the estimation of the latter. the typical population parameter values with relative standard errors (expressed as percent coefficient of variation) are: CL (ml/min) of 0.4 (7.8%), V_{1 male} (ml) of 19.1 (6.7%), and V_{1 female} (ml) of V_{1 male}* 0.8 (10.4%), k₁₂ (h^?1) of 0.01 (15.3%), and k₂₁ (h^?1) of 0.005 (38.5%). Although NONMEM permitted some explanation of variability (in a group of animals (rats) used in this quantic pharmacokinetic study) in terms of sex, efficient partitioning between inter-and residual intra-animal variability would require an increase in the number of samples per animal.     

A pharmacokinetic comparison of anrukinzumab,an anti- IL-13 monoclonal antibody,among healthy volunteers,asthma and ulcerative colitis patients

AimsAnrukinzumab is an anti-IL13 monoclonal antibody. The goals of this study are to characterize the pharmacokinetics of anrukinzumab in healthy volunteers and different disease states and to identify covariates.MethodsA population pharmacokinetic (PK) model was developed in NONMEM, using data from five clinical studies including healthy volunteers, asthma and ulcerative colitis (UC) patients. Different dosing regimens including different routes of administration were also included in the data.ResultsThe PK of anrukinzumab were described by a two compartment model with first order absorption and elimination. The population estimates (relative standard error) of the volumes of distribution in the central (V_c) and peripheral (V_p) compartments were 3.8 (4.6%) and 2.2 l (8.7%), respectively. In non-UC patients, the population estimate of the systemic clearance (CL) and inter-compartmental CL was 0.00732 l h^–1 (4.9%) and 0.0224 l h^–1 (15.4%). For subcutaneous administration, the absorption rate constant was 0.012 h^–1 (6.6%) and bioavailability was nearly 100% in healthy and mild to moderate asthma patients. Both V and CL increased with body weight. CL (but not V) decreased with increasing baseline albumin concentrations. UC patients had an increased CL of 72.3% (10.5%), after correction for differences in body weight and albumin. Moderate to severe asthma patients had decreased bioavailability compared with other populations.ConclusionsAnrukinzumab''s PK behave like a typical antibody. UC patients were identified to have a faster CL of anrukinzumab than healthy volunteers and asthma patients. This finding suggests a higher dose level may be required for this population.     

Population pharmacokinetics of lamotrigine in Indian epileptic patients

Purpose

The aim of this analysis was to describe the pharmacokinetics of oral lamotrigine (LTG) in Indian epileptic patients using a population pharmacokinetic (PPK) modeling approach to confirm that the PK is similar to that of the Caucasian population, and to evaluate and confirm the impact of covariates predictive of inter-individual variability using a simulation platform.

Methods

Blood samples were obtained from 95 patients, and LTG plasma concentrations were determined. Population PK modeling was performed using NONMEM. A one-compartment PK model with first-order absorption and elimination was used to describe the LTG PK. Log-likelihood profiling and normalized prediction distribution errors (NPDE) were used for model evaluation. A simulation study was performed to investigate dose regimens.

Results

Clearance (CL) was estimated to be 2.27 L/h with inter-individual variability (IIV) of 29 CV%. Volume of distribution (V) was estimated to be 53.6 L (31 CV% IIV). Body weight and concurrent use of carbamazepine and valproate were identified as significant covariates on clearance. Log-likelihood profiling indicated that parameters could be estimated with adequate precision, and NPDE indicated that the model adequately described the data observed. The simulation study illustrated the impact of carbamazepine and valproate on LTG PK, and negligible differences in PK between Indian and Caucasian patients.

Conclusions

This is the first PK analysis of LTG in Indian patients. The population PK model developed adequately described the data observed. Comparison of identified PK parameters with previous PK analyses in Caucasian patients indicates that CL of LTG is similar, while V is somewhat lower compared with Caucasian patients, but this is not expected to lead to relevant differences in PK profiles during steady state.     

来氟米特在中国健康人群中的群体药动学研究

目的：建立来氟米特口服给药在中国健康受试者体内的群体药动学模型,探讨其药动学特征及可能的影响因素。方法：21名健康男性受试者参与本次研究,应用Phoenix NLME（Vision 8.0）软件中的群体模块分析来氟米特口服给药后其代谢产物的血药浓度数据,估算相关药动学参数及其变异情况。结果：来氟米特活性代谢产物特立氟胺在健康志愿者中符合一级吸收的一室模型。吸收速率常数K_a、分布容积V、药物清除率CL的群体典型值分别为0.691 h^-1、12.843 L和0.031 L·h^-1。协变量筛选结果显示,BMI对分布容积V有显著影响（P<0.01）。结论：本研究成功建立了来氟米特在中国健康人群中的群体药动学模型,最终模型可对个体药代参数做出精确的估计,BMI对分布容积V有显著影响。     

Population Pharmacokinetic Modeling: The Importance of Informative Graphics

Purpose. The usefulness of several modelling methods were examined in the development of a population pharmacokinetics model for cefepime. Methods. The analysis was done in six steps: (1) exploratory data analysis to examine distributions and correlations among covariates, (2) determination of a basic pharmacokinetic model using the NON-MEM program and obtaining Bayesian individual parameter estimates, (3) examination of the distribution of parameter estimates, (4) multiple linear regression (MLR) with case deletion diagnostics, generalized additive modelling (GAM), and tree-based modelling (TBM) for the selection of covariates and revealing structure in the data, (5) final NONMEM modelling to determine the population PK model, and (6) the evaluation of final parameter estimates. Results. An examination of the distribution of individual clearance (CL) estimates suggested bimodality. Thus, the mixture model feature in NONMEM was used for the separation of subpopulations. MLR and GAM selected creatinine clearance (CRCL) and age, while TBM selected both of these covariates and weight as predictors of CL. The final NONMEM model for CL included only a linear relationship with CRCL. However, two subpopulations were identified that differed in slope and intercept. Conclusions. The findings suggest that using informative graphical and statistical techniques enhance the understanding of the data structure and lead to an efficient analysis of the data.     

Population pharmacokinetics of itraconazole solution used as prophylaxis for febrile neutropenia

Although administration of antifungal agents, such as itraconazole (ITC) solution, for prophylaxis is the most promising strategy for the treatment of haematological malignancies, little is known about the population pharmacokinetic (PK) parameters. A clinical study was conducted to identify PK parameters for the administration of 200 mg/day ITC solution used as prophylaxis for febrile neutropenia in patients undergoing treatment. The study population comprised six patients. NONMEM software was used to estimate PK parameters. Clearance, volume of distribution and the absorption rate constant were 12.7 L/h, 333 L and 1.72 h⁻¹, respectively. These parameters were different from a previous study to large extent, which may be due to differences in intended patients. These differences strongly suggest that establishment of population pharmacokinetics is essential for planning a prospective clinical trial. Assuming a normal distribution, we predicted the trough concentrations of 94.5% of the patients receiving 200 mg/day ITC solution to be >250 ng/mL, indicating that administration of 200 mg/day might be suitable for prophylaxis. This pilot study presents a basic PK model of ITC solution in Japanese haematological patients for the establishment of optimal administration. Large-scale studies will be necessary in the future to determine population PK parameters with covariates.     

Comparison of the Pharmacokinetics of S-1, an Oral Anticancer Agent, in Western and Japanese Patients

Objective: S-1 is an oral anticancer agent combining tegafur (FT), a prodrug of 5-fluorouracil (5-FU), with potassium oxonate (oteracil) and gimeracil (CDHP) respectively to mitigate gastrointestinal toxicity and increase the half-life of 5-FU. This article presents a population pharmacokinetic analysis of these four compounds in Western cancer patients. The second objective was to compare the pharmacokinetics of S-1 in Western and Japanese patients. Methods: A single dose (25–45 mg/m²) of S-1 was administered to 60 patients. In each patient, 6 concentrations of FT, 5-FU, oteracil and CDHP were measured over 24hr. Using NONMEM, oteracil and CDHP were analyzed separately, and the individual estimates of CDHP parameters were included in the joint analysis of FT and 5-FU. We used validation techniques to assess differences between the two populations, and finally we compared the exposures in Western and Japanese patients using simulations. Results: A compartmental model describing the PK of the 4 compounds was developed. The influence of CDHP on the elimination of 5-FU was well described by an enzymatic inhibition model. The model provided a good fit for all compounds. The pharmacokinetics for 5-FU and oteracil were similar between Western and Japanese patients, but apparent differences in exposure to 5-FU resulted from different total doses due to different body sizes.     

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.