Variability in the population pharmacokinetics of pyrazinamide in South African tuberculosis patients

Objective This study was designed to characterize the population pharmacokinetics of pyrazinamide in South African pulmonary tuberculosis patients, with special reference to interindividual and interoccasional variability (IIV and IOV, respectively).Methods Concentration-time measurements obtained from 227 patients receiving oral doses of pyrazinamide were pooled to create a dataset containing 3,092 data points spanning multiple dosing occasions. The software program NONMEM was used to analyze the data.Results A one-compartment model with first-order absorption, including a zero-order component describing release from formulation, and first-order elimination best described the data. The absorption rate constant was estimated to be bimodally distributed between two distinct subgroups, fast and slow, in approximately even proportion. Absorption rate was threefold greater in fast absorbers (3.56 h⁻¹) in comparison to slow absorbers (1.25 h⁻¹). Typical values of oral clearance and apparent volume of distribution were estimated as 3.42 L h⁻¹ and 29.2 l, respectively. IOV was supported in oral clearance (0.0238, variance) and absorption rate (0.623, variance). The duration of zero-order absorption was estimated as 0.290 h, and was quite variable between patients (0.957, variance).Conclusion The absorption of pyrazinamide in the studied population was highly variable and two separate subpopulations were identified. IOV accounted for a proportion of the variability in clearance and the absorption rate constant.An erratum to this article can be found at     

NONMEM法分析静滴异丙酚在中国人体的群体药代动力学

目的　考察中国人静脉匀速滴注异丙酚的群体药代动力学。方法　51例腰麻-硬膜外联合麻醉病人匀速输注异丙酚直至暴发脑电抑制,以HPLC法测定异丙酚血浆浓度,用NONMEM程序分析中国人异丙酚群体药代动力学。结果　异丙酚药代动力学符合三室线性开放模型,群体参数CL(L.min-1)、Vc(L)、Q2(L.min-1)、V2(L)、Q3(L.min-1)和V3(L)的标准值分别为1.10,7.63,1.54,15.0,0.76和175;体重对CL的校正为体重除以60的0.70次方,CL和Q2年龄≥60的病人较年龄<60的分别低18.1%和32.1%;年龄对V2和Q3的校正分别为年龄除以50的-0.66次方和-0.71次方。结论　NONMEM法对以三室模型群体参数估算的血药浓度值与实测值有良好相关性,体重、年龄对参数影响较大。     

The effect of rifampicin and pyrazinamide on isoniazid pharmacokinetics in rats

Tuberculosis chemotherapy involves combination of the drugs isoniazid (INH), rifampicin (RMP) and pyrazinamide (PYR) for a 6-month period. The present work investigated the influence of RMP and PYR on the pharmacokinetic parameters of INH when groups of rats were pre-treated for 21 days with INH alone or in combination with RMP and/or PYR, in the following amounts per kg body weight: INH 100 mg; INH 100 mg+RMP 100 mg; INH 100 mg+PYR 350 mg; INH 100 mg+PYR 350 mg+RMP 100 mg. It was found that the co-administration of PYR caused an increase in the INH distribution volume (V(d)/F), half-life of elimination (t(1/2beta)) and clearance (Cl(T)/F), and a decrease in the area under curve 0 to 24 h (AUC). Co-administration of RMP caused an increase in the Cl(T)/F and a decrease in the AUC. The combination INH+PYR+RMP caused an increase in the Cl(T)/F and a decrease in the AUC. These significant pharmacokinetic interactions between the tuberculostatic drugs might be related to differences in the therapeutic and toxic effects.     

Determination of phenobarbitone population clearance values for South African children

Non-linear Mixed Effects Modelling (NONMEM) was used to estimate phenobarbitone population clearance values for South African children, using 52 serum levels gathered from 32 patients during their routine care. NONMEM was also used to evaluate the influence of fixed effects such as weight, age and concomitant medication. The final model describing phenobarbitone clearance was CL=[Exp(0.0288 Wt–2.53)] M, where CL=clearance (l·h^–1), Exp=the base of the natural logarithm, Wt=patient weight (kg) and M=a scaling factor for concomitant medication with a value of 1 for patients on phenobarbitone monotherapy, 0.62 for those receiving concomitant valproate and 0.87 for those patients receiving concomitant carbamazepine or phenytoin. Mean (95% confidence interval) phenobarbitone clearance values were 7.6 ml·h^–1·kg^–1 (6.2, 9.0 ml·h^–1·kg^–1) for the monotherapy group, 5.0 ml·h^–1·kg^–1 (4.0, 6.0 ml·h^–1·kg^–1) in the presence of concomitant valproate and 6.8 ml·h^–1·kg^–1 (5.6, 8.0 ml·h^–1·kg^–1) in the presence of concomitant carbamazepine or phenytoin. These values are similar to those previously reported from both traditional and NONMEM pharmacokinetic studies.     

N-乙酰化酶2基因型对中国肺结核患者异烟肼代谢的影响

目的研究N-乙酰化酶2(NAT2)基因型对中国肺结核患者异烟肼(INH)代谢的影响。方法采用反向点交法(RDB)检测中国肺结核患者NAT2基因型;柱前衍生化高效液相色谱法检测服药2 h后血浆中INH及其代谢物乙酰化INH(Ac- INH)浓度。结果46例患者基因型包括野生型wt/wt(n=17)、杂合子m/wt(n=22)、突变型纯合子m/m(n=7)。血浆INH及AcINH浓度分别为(12.74±10.51)和(12.49±9.61)μmol·L~(-1)。3个基因组INH、AcINH浓度比为1:1.37:1.77和1:0.77:0.75;3组AcINH与INH比值(R_(A/I))为1:0.52:0.40(P<0.01)。结论不同NAT2基因型的结核患者对INH代谢能力差异显著,存在基因剂量现象。NAT2基因分型对结核患者合理用药具有重要意义。     

群体药动学及其应用研究进展

概述了群体药动学的研究方法,着重介绍了群体药动学的原理、步骤及应用。近年来群体药动学应用范围不断拓宽,极大地推进了个体化用药的发展,已成为临床药代动力学研究的重要手段。     

美罗培南的群体药动/药效学研究进展

目的：简述美罗培南的药动学和药效学基本特点,介绍群体药动学研究基本理论,重点阐述美罗培南的群体药动/药效学研究状况。方法：查阅近年关于美罗培南群体药动/药效学文献,提取最终模型以及给药方案,分析归纳并综述。结果：美罗培南的药动学特征是二房室模型,药效学考察% T>MIC。婴幼儿和老年人的给药方案需要调整,未来的研究将关注肾功能特殊的患者以及体液体积大的患者。结论：需要研究正常脂肪体重（NFM）与美罗培南的群体药动/药效学的关系。     

Pharmacokinetics of isoniazid: Influence of age

Summary The distribution of the acetylator phenotype of isoniazid was studied in 458 patients of different ages, and the influence of age on its apparent distribution volume, clearance and half-life was investigated in slow and rapid acetylators. The doses of isoniazid for the patients were determined according to the inactivation index method, as described by Vivien. Apparent distribution volume showed no difference between slow and rapid acetylators but it did decrease significantly with age. Clearance and half-life varied significantly in slow acetylators, and these variations led to a decrease in the necessary dose of isoniazid.     

建立阿奇霉素在中国健康人群中的群体药代动力学模型

目的建立中国人群中阿奇霉素(大环内酯类抗生素)的群体药代动力学模型。方法对20例健康自愿者的血药浓度和生化指标,用非线性混合效应模型法进行群体药代动力学分析,估算药代动力学参数,分析固定效应的影响以及个体内/间的变异,建立群体药代动力学模型。结果口服阿奇霉素呈一级吸收的二室模型,体质量对CL1和CL2及年龄对V1均有影响。结论用非线性混合效应模型法建立的中国人群中阿奇霉素的群体药代动力学模型,结构稳定,预测准确。     

双环醇对利福平和异烟肼在大鼠体内药代动力学的影响

目的：研究双环醇对利福平和异烟肼血药浓度及药代动力学参数的影响。方法：应用HPLC法测定与双环醇联用前后利福平和异烟肼的血药浓度,以DAS2．0药代动力学程序拟合药动学参数。结果：双环醇与利福平合用、双环醇与异烟肼合用、双环醇与利福平和异烟肼同时合用的各时间点中,除异烟肼6h的血药浓度三药合用组与其他组有显著性差异（P〈0．05）之外,其余时间点的血药浓度值在各组间均无显著性差异（P〉0．05）;药动学参数AUC（药时曲线下面积）（0-t）、AUC（0-∞）、MRT（体内平均驻留时间）（0-t）、MRT（0-∞）、t1/2x（半衰期）、tmax（达峰时间）、CLx/F（清除率）、Vx/F（表现分布容积）、Cmax（血药峰浓度）各组间均无显著性差异（P〉0．05）。结论：双环醇与利福平合用或与异烟肼合用,以及与利福平和异烟肼两药合用,均未见对利福平和异烟肼药动参数有明显影响。     

High dose methotrexate population pharmacokinetics and Bayesian estimation in patients with lymphoid malignancy

The purpose of present study was to develop a population pharmacokinetic model of high dose methotrexate (HD‐MTX) infusion in patients with lymphoid malignancy, to investigate the biological and clinical covariates related to the drug distribution and elimination. It is also the purpose to propose a limited sampling strategy (LSS) for the estimation of the time above the threshold (0.2 µmol·L^?1). A total 82 patients with lymphoid malignancy were involved in the study. A pharmacokinetic model was developed using nonlinear mixed‐effect model. The influence of demographic characteristics, biological factors, and concurrent administration were investigated. The final predictive performance was validated by bootstrap and cross‐validation. Bayesian estimation was evaluated. The pharmacokinetics of HD‐MTX was described by a two‐compartment model. The pharmacokinetic parameters and the inter‐individual variability were as follows: the clearance CL, 7.45 L·h^?1 (inter‐individual variability 50.6%), the volume of the central and peripheral compartment V₁, 25.9 L (22.5%), V₂, 9.23 L (97.8%), respectively, and the intercompartmental clearance Q, 0.333 L·h^?1 (70.4%). The influence of serum creatinine on CL and weight on V₁ was retained in the final model. The protocol involved one sampling time at 44 h after the start of the infusion, allowing one to predict the time at which the MTX concentration reached the expected threshold (0.2 µmol·L^?1). Serum creatinine and weight showed significant influence on methotrexate CL and V₁, respectively. Furthermore, a Bayesian estimation based on the covariates and 44 h sample was developed, allowing prediction of the individual methotrexate pharmacokinetic parameters and the time to 0.2 µmol·L^?1. Copyright © 2009 John Wiley & Sons, Ltd.     

Population pharmacokinetics of arbekacin in burn patients

The aim of this study was to estimate the pharmacokinetics (PK) of arbekacin in burn patients using a population–PK approach. Therapeutic drug monitoring data consisting of 126 plasma concentrations (including 17 values that were below the quantitation limit) from 47 burn patients were retrospectively analyzed using a mixed effect method (NONMEM, ver. 6.0). Covariates, such as burn index, age, sex, among others, were tested on the basic one-compartment model. In the basic model, positive correlations of body weight (WT) and creatinine clearance (CLcr) on total clearance (CL) and volume of distributions (V) were assumed. In the final model, V increased with burn index (BI). The final model was: ;. Between-subject variability in terms of CL and V were 35 and 39%, respectively. The CL of our burn patients was significantly greater than that reported in unburned patients, and V increased proportionally with increasing BI.     

Statistical estimations in pharmacokinetics

Several important statistical aspects of pharmacokinetic analyses by digital computer are discussed. These include selection of appropriate equations, weighting of data, precision of parameter estimates, comparisons of parameters, analysis of weighted residuals, and criteria useful in the selection of particular models. Data obtained after administration of isoniazid and isonicotinuric acid to man are analyzed to illustrate the usefulness of the discussed methods.     

老年心衰患者口服地高辛群体药动学模型的建立

目的:应用非线性混合效应模型计算国人老年心衰患者口服地高辛(digxion)群体药动学参数,以促进个体化给药。方法:采用荧光偏振免疫法(FPIA)测定84例老年患者120例次地高辛的血清浓度并收集相关临床指标,运用NONMEM软件建立群体药动学模型。结果:地高辛的药动学符合一室线性开放模型,固定效应参数中,体质量、剂量、血肌酐及尿素氮对参数有影响。最终回归模型中地高辛血药浓度估算值与实测浓度间线性关系良好。结论:用群体药动学模型分析常规监测数据可为老年患者个体化给药提供依据。     

A population analysis of the pharmacokinetics and pharmacodynamics of midazolam in the rat

The concentration-EEG effect relationship of midazolam in the rat was studied from a population perspective. Plasma concentration and EEG effect data from 27 rats were available for analysis. Effect parameters derived from aperiodic EEG analysis were used as effect parameters. The population analysis gave results that were similar to the sample theory estimates (¯xs and SDs) obtained from the fits to individual data sets. Reanalysis of the EEG data using mean population pharmacokinetic parameters as input to the pharmacodynamic model led to poorer estimation of the pharmacodynamic parameters: particularly EC₅₀.Inclusion of one observed plasma concentration per individual significantly improved the estimation of the pharmacodynamic parameters and led to results that were virtually indistinguishable from those obtained using complete pharmacokinetic data.This study was supported by Medigon grant 900-521-106.     

Transfer of isoniazid from circulation to breast milk in lactating women on chronic therapy for tuberculosis

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT
• Isoniazid is the most widely used first line antituberculosis drug.
• It is considered safe during lactation, but limited data are available on the transfer of isoniazid from circulation to milk in lactating women, which can provide an assessment of extent of exposure to the nursling.
WHAT THIS STUDY ADDS
• The study documents the transfer pattern and milk to plasma (M : P) ratio of isoniazid at a steady state.
• Peak plasma and milk concentrations of isoniazid were reached within 1 h and the projected exposure of the drug to the infant is much lower than the prophylactic dose, supporting its safety during breast feeding.  

AIM

To determine milk to plasma (M : P) ratios and infant dose (absolute and relative) for isoniazid in lactating women on antituberculosis therapy.  

METHODS

Concentrations of isoniazid in plasma and milk were measured in exclusively breast feeding women taking 300 mg day⁻¹ as treatment for tuberculosis.  

RESULTS

Peak plasma and milk concentrations of isoniazid were observed at 1 h. A mean M : P_AUC value of 0.89 (95% CI 0.7, 1.1) was calculated for isoniazid from seven women over 24 h. The mean absolute infant dose was estimated to be 89.9 μg kg day⁻¹ (95% CI 65.6, 114) and the relative infant dose was 1.2% of the weight adjusted maternal dose.  

CONCLUSIONS

The mean relative dose of isoniazid (1.2%) transmitted to the infant via breast milk is below the 10% notional level of concern. These data suggest that isoniazid therapy is safe during breastfeeding.     

Experimental design and efficient parameter estimation in population pharmacokinetics

A computer simulation technique used to evaluate the influence of several aspects of sampling designs on the efficiency of population pharmacokinetic parameter estimation is described. Although the simulations are restricted to the one-compartment one-exponential model, they provide the basis for a discussion of the structural aspects involved in designing a population study. These aspects include number of subjects required, number of samples per subject, and timing of these samples. Parameter estimates obtained from different sampling schedules based on two- and three-point designs are evaluated in terms of accuracy and precision. These simulated data sets include noise terms for both inter- and intraindividual variability. The results show that the population fixed-effect parameters (mean clearance and mean volume of distribution) for this simple pharmacokinetic model are efficiently estimated for most of the sampling schedules when two or three points are used, but the random-effect parameters (describing inter- and intraindividual variability) are inaccurate and imprecise for most of the sampling schedules when only two points are used. This drawback was remedied by increasing the number of data points per individual to three.Supported by the Scottish Home and Health Department (Biomedical Research Committee).     

Dose optimization with population pharmacokinetics of ritonavir-boosted lopinavir for Thai people living with HIV with and without active tuberculosis

BackgroundPrior to dolutegravir availability, ritonavir-boosted lopinavir (LPV/r) was an alternative recommendation when first-line drugs could not be used. A high concentration of protease inhibitors was observed in the Thai people living with HIV (PLWH). Thus, dose reduction of LPV/r may be possible. However, the pharmacokinetics and dose optimization of LPV/r have never been investigated. This study aimed to develop a population pharmacokinetic model of LPV/r and provide dosage optimization in Thai PLWH.MethodsLPV and RTV trough concentrations from Thai PLWH were combined with intensive data. The data were analyzed by the nonlinear mixed-effects modeling approach. The influence of RTV concentration on LPV oral clearance (CL/F) was investigated.ResultsRifampicin (RIF) use increased LPV and RTV CL/F by 2.16-fold and 1.99-fold, respectively. The reduced dose of 300/75 and 200/150 mg twice daily provided a comparable percentage of patients achieving LPV target trough concentration to the standard dose for PI-naïve patients. For HIV/TB co-infected patients receiving RIF who could not tolerate the recommended dose, the reduced dose of 600/150 mg twice daily was recommended.ConclusionThe population pharmacokinetic model was developed by integrating the interaction between LPV and RTV. The reduced LPV/r dosage offers sufficient LPV exposure for Thai PLWH.     

The population pharmacokinetics of R- and S-warfarin: effect of genetic and clinical factors

BACKGROUND

Warfarin is a drug with a narrow therapeutic index and large interindividual variability in daily dosing requirements. Patients commencing warfarin treatment are at risk of bleeding due to excessive anticoagulation caused by overdosing. The interindividual variability in dose requirements is influenced by a number of factors, including polymorphisms in genes mediating warfarin pharmacology, co-medication, age, sex, body size and diet.

AIMS

To develop population pharmacokinetic models of both R- and S-warfarin using clinical and genetic factors and to identify the covariates which influence the interindividual variability in the pharmacokinetic parameters of clearance and volume of distribution in patients on long-term warfarin therapy.

METHODS

Patients commencing warfarin therapy were followed up for 26 weeks. Plasma warfarin enantiomer concentrations were determined in 306 patients for S-warfarin and in 309 patients for R-warfarin at 1, 8 and 26 weeks. Patients were also genotyped for CYP2C9 variants (CYP2C9*1,*2 and *3), two single-nucleotide polymorphisms (SNPs) in CYP1A2, one SNP in CYP3A4 and six SNPs in CYP2C19. A base pharmacokinetic model was developed using NONMEM software to determine the warfarin clearance and volume of distribution. The model was extended to include covariates that influenced the between-subject variability.

RESULTS

Bodyweight, age, sex and CYP2C9 genotype significantly influenced S-warfarin clearance. The S-warfarin clearance was estimated to be 0.144 l h⁻¹ (95% confidence interval 0.131, 0.157) in a 70 kg woman aged 69.8 years with the wild-type CYP2C9 genotype, and the volume of distribution was 16.6 l (95% confidence interval 13.5, 19.7). Bodyweight and age, along with the SNPs rs3814637 (in CYP2C19) and rs2242480 (in CYP3A4), significantly influenced R-warfarin clearance. The R-warfarin clearance was estimated to be 0.125 l h⁻¹ (95% confidence interval 0.115, 0.135) in a 70 kg individual aged 69.8 years with the wild-type CYP2C19 and CYP3A4 genotypes, and the volume of distribution was 10.9 l (95% confidence interval 8.63, 13.2).

CONCLUSIONS

Our analysis, based on exposure rather than dose, provides quantitative estimates of the clinical and genetic factors impacting on the clearance of both the S- and R-enantiomers of warfarin, which can be used in developing improved dosing algorithms.