Population pharmacokinetics of itraconazole in Thai HIV-1-infected persons

The authors describe the development of a population pharmacokinetic model using NONMEM for itraconazole and its active metabolite hydroxyitraconazole in a Thai cohort of HIV-infected patients who were using itraconazole as an addition to their antiretroviral therapy. The data were best described with an open two-compartment model for both itraconazole and hydroxyitraconazole. The model adequately described the data and provided population pharmacokinetic parameters which were not different from those described for other populations. The authors found that concomitant use of co-trimoxazole leads to a reduced formation rate (-51%) of hydroxyitraconazole.     

Population pharmacokinetics of efavirenz in an unselected cohort of HIV-1-infected individuals

OBJECTIVE: The aim of this study was to characterise the population pharmacokinetics of efavirenz in a representative patient population and to identify patient characteristics influencing the pharmacokinetics of efavirenz, with the ultimate goal of further developing techniques that can be applied to optimise therapeutic drug monitoring of antiretroviral agents. METHODS: Ambulatory HIV-1-infected patients using an efavirenz-containing regimen were included. During regular visits, blood samples were collected for efavirenz plasma concentrations and clinical chemistry parameters. Concentrations of efavirenz were quantitatively assessed by a validated high-performance liquid chromatographic with ultraviolet detection method. Using nonlinear mixed-effect modelling (NONMEM), the pharmacokinetics of efavirenz were described. Disposition of efavirenz was described by a two-compartment model and absorption was modelled using a chain of three transition compartments. Apparent clearance (CL/F), volume of distribution after oral administration (V(d)/F), intercompartmental clearance, the peripheral volume of distribution and the intercompartmental transition rate constant (k(tr)) were estimated. Furthermore, interindividual, interoccasion and residual variability were estimated. The influence of patient characteristics on the pharmacokinetic parameters of efavirenz was explored. RESULTS: From 172 patients, 40 full pharmacokinetic curves and 315 efavirenz plasma concentrations at a single timepoint were available, resulting in a database of 1009 efavirenz plasma concentrations. CL/F, V(d)/F, and k(tr) were 11.7 L/h (4.3% relative standard error [RSE]), 189L (14.6% RSE) and 3.07 h(-1) (11.2% RSE), respectively. Residual variability in the model was composed of 0.14 mg/L additive error and 8.85% proportional error. Asian race and baseline total bilirubin (TBR) increased the relative bioavailability of efavirenz by 56% and 57%, respectively. No significant covariates were found for CL/F or V(d)/F. CONCLUSION: The pharmacokinetic parameters of efavirenz were adequately described with the developed population pharmacokinetic model. Asian race and baseline TBR were found to be significantly correlated with the bioavailability of efavirenz. The described model will be an essential tool in further optimisation of efavirenz-containing antiretroviral therapy, e.g. by the use of Bayesian estimation of individual pharmacokinetic parameters.     

Population pharmacokinetics of nevirapine in an unselected cohort of HIV-1-infected individuals

AIMS: To study the population pharmacokinetics of nevirapine and to identify relationships between patient characteristics and pharmacokinetics in an unselected population of patients attending our outpatient clinic. METHODS: Ambulatory HIV-1-infected patients from the outpatient clinic of the Slotervaart Hospital who were being treated with a nevirapine-containing regimen were included. During each visit, blood samples were collected for the determination of nevirapine plasma concentrations and clinical chemistry parameters. Variables that were collected at baseline were serology for hepatitis B (HBV) and C (HCV) viruses, liver enzymes, and total bilirubin (TBR). In addition, information about concomitant use of St John's wort and patient demographics were included. The pharmacokinetics of nevirapine were described by first-order absorption and elimination using nonlinear mixed effect modelling (NONMEM V1.1). Population pharmacokinetic parameters (apparent clearance (CL/F), volume of distribution (V/F), absorption rate constant (k a)) were estimated, as were interindividual, interoccasion, and residual variability in the pharmacokinetics. The influence of patient characteristics on the pharmacokinetics of nevirapine was determined. RESULTS: From 173 outpatients a total number of 757 nevirapine plasma concentrations at a single random time point and full pharmacokinetic curves for 13 patients were available resulting in a database of 1329 nevirapine plasma concentrations. Mean CL/F, V/F, and k a were 3.27 l h-1, 106 l, and 01.66 h-1, respectively. CL/F of nevirapine was correlated with weight, chronic HCV infection, and baseline aspartate aminotransferase (ASAT). Chronic HCV and baseline ASAT> 1.5 x upper limit of normal (ULN) decreased CL/F by 27.4% and 13.2%, respectively, whereas an increase in body weight of 10 kg increased CL/F by 0.14 l h-1. A trend towards a lower CL/F in patients of the Negroid race was observed. No significant covariates were found for V/F. CONCLUSIONS: The pharmacokinetics of nevirapine were adequately described by our population pharmacokinetic model. Weight, chronic HCV infection, and baseline ASAT were found to be significant covariates for CL/F of nevirapine. The model incorporating these significant covariates may be an important aid in further optimizing nevirapine-containing therapy.     

Population pharmacokinetics of atazanavir/ritonavir in HIV-1-infected children and adolescents

AIMS

To investigate atazanavir (ATV) population pharmacokinetics in children and adolescents, establish factors that influence ATV pharmacokinetics and investigate the ATV exposure after recommended doses.

METHODS

Atazanavir concentrations were measured in 51 children/adolescents during a mean therapeutic monitoring follow up of 6.6 months. A total of 151 ATV plasma concentrations were obtained, and a population pharmacokinetic model was developed with NONMEM. Patients received ATV alone or boosted with ritonavir.

RESULTS

Atazanavir pharmacokinetics was best described by a one-compartment model with first-order absorption and elimination. The effect of bodyweight was added on both apparent elimination clearance (CL/F) and volume of distribution using allometric scaling. Atazanavir CL/F was reduced by ritonavir by 45%. Tenofovir disoproxil fumarate (TDF) co-medication (300 mg) increased significantly by 25% the atazanavir/ritonavir (ATV/r) CL/F. Mean ATV/r CL/F values with or without TDF were 8.9 and 7.1 L h⁻¹ (70 kg)⁻¹, respectively. With the recommended 250/100 mg and 300/100 mg ATV/r doses, the exposure was higher than the mean adult steady-state exposure in the bodyweight range of 32–50 kg.

CONCLUSIONS

To target the mean adult exposure, children should receive the following once-daily ATV/r dose: 200/100 mg from 25 to 39 kg, 250/100 mg from 39 to 50 kg and 300/100 mg above 50 kg. When 300 mg TDF is co-administered, children should receive (ATV/r) at 250/100 mg between 35 and 39 kg, then 300/100 mg over 39 kg.     

Lack of interaction between enfuvirtide and ritonavir or ritonavir-boosted saquinavir in HIV-1-infected patients

Enfuvirtide (Fuzeon) is an HIV fusion inhibitor, the first drug in a new class of antiretrovirals. The HIV protease inhibitors ritonavir and saquinavir both inhibit cytochrome P450 (CYP450) isoenzymes, and low-dose ritonavir is often used to boost pharmacokinetic exposure to full-dose protease inhibitors. These two studies were designed to assess whether ritonavir and ritonavir-boosted saquinavir influence the steady-state pharmacokinetics of enfuvirtide. Both studies were single-center, open-label, one-sequence crossover clinical pharmacology studies in 12 HIV-1-infected patients each. Patients received enfuvirtide (90 mg twice daily [bid], subcutaneous injection) for 7 days and either ritonavir (200 mg bid, ritonavir study, orally) or saquinavir/ritonavir (1000/100 mg bid, saquinavir/ritonavir study, orally) for 4 days on days 4 to 7. Serial blood samples were collected up to 24 hours after the morning dose of enfuvirtide on days 3 and 7. Plasma concentrations for enfuvirtide, enfuvirtide metabolite, saquinavir, and ritonavir were measured using validated liquid chromatography tandem mass spectrometry methods. Efficacy and safety were also monitored. Bioequivalence criteria require the 90% confidence interval (CI) for the least squares means (LSM) of C(max) and AUC(12h) to be between 80% and 125%. In the present studies, analysis of variance showed that when coadministered with ritonavir, the ratio of LSM for enfuvirtide was 124% for C(max) (90% confidence interval [CI]: 109%-141%), 122% for AUC(12h) (90% CI: 108%-137%), and 114% for C(trough) (90% CI: 102%-128%). Although the bioequivalence criteria were not met, the increase in enfuvirtide exposure was small (< 25%) and not clinically relevant. When administered with ritonavir-boosted saquinavir, the ratio of LSM for enfuvirtide was 107% for C(max) (90% CI: 94.3%-121%) and 114% for AUC(12h) (90% CI: 105%-124%), which therefore met bioequivalence criteria, and 126% for C(trough) (90% CI: 117%-135%). The pharmacokinetics of enfuvirtide are affected to a small extent when coadministered with ritonavir at a dose of 200 mg bid but not when coadministered with a saquinavir-ritonavir combination (1000/100 mg bid). However, previous clinical studies have shown that such increases in enfuvirtide exposure are not clinically relevant. Thus, no dosage adjustments are warranted when enfuvirtide is coadministered with low-dose ritonavir or saquinavir boosted with a low dose of ritonavir.     

The pharmacokinetics of nelfinavir in HIV-1-infected children

The authors investigated the steady-state plasma pharmacokinetics of nelfinavir in HIV-1-infected children in a dosage of 30 mg/kg every 8 hours and 45 mg/kg every 12 hours in 12 HIV-1-infected children (aged 2.1 to 10.8 years) participating in an open-label study of nelfinavir in combination with stavudine and lamivudine.Median values of the primary pharmacokinetic parameters of nelfinavir 30 mg/kg every-8-hours (n = 8) and 45 mg/kg every 12 hours (n = 10) were, respectively, for the area under the plasma concentration-time curve over 24 hours, 90.5 and 71.9 h x microg/mL, for the trough concentration 1.9 and 1.0 microg/mL, and for the maximal concentration 6.3 and 5.2 microg/mL. Overall, a 7-fold interpatient variability was observed for the exposure to nelfinavir. Nelfinavir 30 mg/kg every-8-hours or 45 mg/kg every 12 hours in HIV-1-infected children generally resulted in plasma concentrations higher than those obtained in adults. However, due to a large interpatient variability in the exposure, individual dosage adjustments based on plasma concentrations may be necessary for both dosing regimens to ensure optimal treatment.     

Population pharmacokinetics of digoxin in pediatric patients

Digoxin pharmacokinetics were studied in a pediatric population with an age range of 6 days to 1 year using the population pharmacokinetic approach. Digoxin data were analyzed by mixed-effects modeling according to a one-compartment steady-state pharmacokinetic model using NONMEM software. The final model selected for the population prediction of digoxin clearance in pediatric patients was as follows: [equation: see text] Individual empirical Bayesian estimates were generated on the basis of the population estimates and were used to correlate the optimum dose of digoxin and patient age according to the following equation: [equation: see text] This equation and its derived nomogram may be used for the initial dosing of digoxin in children aged between 0 and 1 year. The use of this nomogram in routine monitoring requires further pharmacokinetic and clinical validation.     

Population pharmacokinetics of ciprofloxacin in pediatric patients

The objective of this study was to characterize ciprofloxacin population pharmacokinetics in pediatric patients. A total of 150 pediatric patients (including 28 patients with cystic fibrosis [CF], ages 0.27-16.9 years) received ciprofloxacin by the oral and/or intravenous routes. Population pharmacokinetic analyses were performed with NONMEN software. Exponential error models were used to describe the interindividual variance in pharmacokinetic parameters, and the residual error model included both proportional and additive components. Based on principles of allometry, the patient's body weight was used as a covariate, along with appropriate allometric exponents, in the construction of the base model. Model building was accomplished by a stepwise forward inclusion procedure, and the final model was evaluated by multiple techniques, including bootstrap, leverage analysis, and cross-validation. With body weight included in the model (two compartments with first-order absorption), ciprofloxacin clearance was influenced by age, and the absorption rate constant was altered in CF patients. The final model is summarized as follows: CL(L/h) = 30.3 x (WT/70)0.75 x (1 + 0.045 [AGE-2.5]), VC(L) = 56.7 x (WT/70)1.0, VP(L) = 89.8 x (WT/70)1.0, Q(L/h) = 37.5 x (WT/70)0.75, Ka (1/h) = 1.27 x (1 + [-0.611 x CF]), absorption lag time = 0.35 hours, and bioavailability fraction = 61.1%, where WT and AGE are the patient's body weight (kg) and age (years), respectively, and the variable CF equals 1 for CF patients and 0 for non-CF patients. The interpatient variability in pharmacokinetic parameters (percentage coefficient of variation [%CV]) ranged from 22.5% to 49.8%. The residual variabilities (%CV) for the oral and intravenous data were 40% and 27%, respectively. The shared additive residual variance component was small (SD = 0.04 mg/L). Model evaluation by the different methods indicated that the final model was robust and parameter estimates were precise. A small difference (< 6%) was noted when the patient's age was not used in dose calculation. Therefore, in routine clinical use, for pediatric patients older than 3 months, ciprofloxacin dose may be calculated solely based on body weight.     

儿童丙戊酸群体药动学

目的:研究仅有临床稀疏数据的儿童丙戊酸群体药动学.方法:收集667例儿童癫痫患者的常规治疗药物监测资料,将794对血药浓度-时间数据利用群体药动学理论经CPKDP程序处理,提取儿童群体药动学参数,再经Bayesian反馈法及二步迭代计算出儿童个体药动学参数.结果:儿童丙戊酸群体药动学主要参数Ke、Vm、CL在单用丙戊酸组分别为(4.5±2.2)h-1、(1.4±0.5)L·kg-1和(14.5±4.3)mL·h-1·kg-1;在合并其他抗癫痫药物时分别为(7.3±3.4)h-1、(1.4±0.6)L·kg-1、(24.8±9.3)mL·h-1·kg-1.预测浓度和实测浓度显著相关;合并PB、PTH、CBZ、CNP对丙戊酸的药动学有显著影响.结论:本研究对儿童丙戊酸给药方案个体化提供有价值的参考依据.     

Immune reconstitution in HIV-1-infected patients

HIV-1-specific CD8 cytotoxic and CD4 helper T-lymphocytes, which are respectively the central effector and regulatory cells in viral infections, together with fully functional antigen-presenting cells, are essential at all stages of HIV-1 infection to control viral activity. Recent studies indicate that such protective HIV-1-specific immune responses can be preserved/induced in HIV-1-infected individuals, utilizing strategies such as treatment interruption after early HAART. Despite successful combination antiretroviral drug therapy, strong anti-HIV-1 T-cell responses are often not apparent in chronic HIV-1 infection, diminishing the probability of viral eradication. Thus, the therapeutic use of immunization and cytokines are required to induce and steer immunity towards a desirable outcome. Here, we review and discuss therapeutic immunization and immunotherapy with regard to their potential use in the treatment of chronic HIV-1 infection.     

Population pharmacokinetics and pharmacodynamics of meropenem in pediatric patients

Meropenem is a highly potent carbapenem antibiotic against gram-positive and gram-negative bacteria. Meropenem plasma concentration data from 99 pediatric patients (aged 0.08-17.3 years) were used to develop a population pharmacokinetic model. Pharmacokinetic analysis was performed using NONMEM with exponential interindividual variability and combinational residual error model. A 2-compartment model was found to fit the data best. Creatinine clearance and body weight were the most significant covariates explaining variabilities in meropenem pharmacokinetics among pediatric patients. The validated final model was used to predict meropenem plasma concentrations in 37 pediatric meningitis patients, receiving 40 mg/kg meropenem, who had minimum inhibitory concentration values of the causative pathogens and outcome available. Since the causative pathogens in all patients were eradicated, no break points for required exposure could be found. The microbiological outcomes indicate that the current clinical dosage regimen provides sufficient drug exposure to eradicate the pathogens commonly involved in pediatric meningitis.     

左乙拉西坦在癫痫患儿中的群体药动学研究

目的建立癫痫患儿口服左乙拉西坦的群体药动学(PPK)模型,并用此模型探讨左乙拉西坦在儿童患者群体内的药动学特征。方法收集344例癫痫患儿口服左乙拉西坦后的血药浓度数据和临床资料。将患儿随机分为两组,模型组(n=259)采用NLME程序进行PPK分析,建立一房室药动学模型(个体间变异采用指数模型,残差变异采用加法模型表示),考察各协变量对参数Ka、Vd和CL的影响。用拟合优度、自举法对最终模型的性能进行内部验证。采用最终模型预测验证组(n=85)患儿的血药浓度,计算平均预测误差(MPE)、平均绝对预测误差(MAE)、平均预测误差平方(MSE)和均方根预测误差(RMSE)对最终模型进行外部验证。结果 PPK最终模型为:Ka(h-1)=1.01×eηKa,Vd(L·kg-1)=[0.42+0.000 35×(AGE-56)]×eηVd,CL(L·kg-1·h-1)=[0.05-0.009 5×(ln WT-2.83)]×eηCl;年龄(AGE)正相关影响Vd,体重的自然对数值(ln WT)负相关影响CL。拟合优度、自举验证的评价结果表明最终模型稳定、预测结果可靠。外部验证最终模型结果为:MPE=0.01 mg·L-1,MAE=0.91 mg·L-1,MSE=1.16(mg·L-1)2,RMSE=1.08 mg·L-1。血药浓度实测值和最终模型的个体预测值的决定系数R2=0.990 6。外部验证说明最终模型预测准确度高。结论本研究成功建立了癫痫患儿口服左乙拉西坦后的PPK模型,模型结构表明左乙拉西坦体重校正的清除率随患儿年龄和体重的增加有下降趋势。     

Long-term zidovudine treatment of asymptomatic HIV-1-infected subjects

Eighteen asymptomatic men with persistent human immunodeficiency virus type 1 (HIV-1) p24 antigenemia were treated with zidovudine 250-500 mg (+/- acyclovir 800 mg) 6-hourly for 4-12 weeks, and thereafter with zidovudine 500 mg (+/- acyclovir 1600 mg) 12-hourly for 92 weeks. Six additional HIV-1 p24 antigenemic subjects were treated with zidovudine 500 mg 12-hourly for 76 weeks. Disease progression occurred in 4 subjects, despite sustained reduction of serum HIV-1 p24 antigen levels: Pneumocystis carinii pneumonia was diagnosed after 60, 80, 90 and 93 weeks, respectively. The median CD4+ cell count of these 4 men at study entry was 0.2 x 10(9)/l, and it declined to 0.07 x 10(9)/l at the moment AIDS was diagnosed. In 20 subjects no disease progression occurred. The median CD4+ cell count of these 20 men at study entry was 0.4 x 10(9)/l and it was 0.45 x 10(9)/l at the end of the study period. Median serum HIV-1 p24 antigen levels at the end of the study period were 42% lower than at study entry in these 20 subjects. In 5/20 men, an initial decline was followed by a rise in antigen levels to above pretreatment value. Treatment with zidovudine was well tolerated. Anemia caused symptoms in 3/24 men, but prolonged leucopenia or neutropenia did not occur. None developed clinical or convincing biochemical evidence of zidovudine-associated myopathy.     

The effect of fluconazole on ritonavir and saquinavir pharmacokinetics in HIV-1-infected individuals

AIMS: To study the effect of fluconazole on the steady-state pharmacokinetics of the protease inhibitors ritonavir and saquinavir in HIV-1-infected patients. METHODS: Five subjects treated with saquinavir and three with ritonavir received the protease inhibitor alone (saquinavir 1200 mg three times daily, ritonavir 600 mg twice daily) on day 1, and the same protease inhibitor in combination with fluconazole (400 mg on day 2 and 200 mg on days 3 to 8). Pharmacokinetic parameters were determined on days 1 and 8. RESULTS: In the saquinavir group, the median increase in the area under the plasma concentration vs time curve was 50% from 1800 microg l(-1) h to 2700 microg l(-1) h (P = 0.04, median increase: 900 microg l(-1) h; 2.5 and 97.5 percentile: 500-1300), and 56% for the peak concentration in plasma (from 550 to 870 microg l(-1), P = 0.04; median increase: 320 microg l(-1) h, 2.5 and 97.5 percentile: 60-450 microg l(-1)). In the ritonavir group, there were no detectable changes in the pharmacokinetic parameters on addition of fluconazole. CONCLUSIONS: Because of the favourable safety profile of saquinavir, dose adjustments are probably not necessary with concomitant use of fluconazole, as is the case for ritonavir.     

HIV进入抑制剂研究进展

HIV进入抑制剂主要干预病毒包膜与靶细胞膜融合过程,可有效预防HIV感染。在HIV进入细胞过程中,HIV包膜糖蛋白gp120首先与宿主细胞膜上的CD4分子结合,使gp120构型变化,继而与CCR5或CXCR5等辅助受体结合,诱使跨膜亚基gp41构型改变,HIV包膜与细胞膜空间靠近,最终融合。基于这一过程,可通过筛选与gp120结合的化合物、设计CD4模拟物、研制CD4或CCR5单抗、构建辅助受体抑制剂等方法,从各个方面干预HIV的进入。对HIV进入抑制剂的靶标和药物研发进展进行概述。