scholarly journals Population Pharmacokinetics of Nevirapine, Zidovudine, and Didanosine in Human Immunodeficiency Virus-Infected Patients

1999 ◽  
Vol 43 (1) ◽  
pp. 121-128 ◽  
Author(s):  
Xiao-Jian Zhou ◽  
Lewis B. Sheiner ◽  
Richard T. D’Aquila ◽  
Michael D. Hughes ◽  
Martin S. Hirsch ◽  
...  
Keyword(s):  
Human Immunodeficiency Virus ◽  
Body Weight ◽  
Population Pharmacokinetics ◽  
Compartment Model ◽  
Volume Of Distribution ◽  
Zero Order ◽  
Triple Combination ◽  
Entire Study ◽  
First Order ◽  
Immunodeficiency Virus

ABSTRACT The population pharmacokinetics of nevirapine (NVP), zidovudine (ZDV), and didanosine (ddI) were evaluated in a total of 175 patients infected with human immunodeficiency virus randomized to receive either a double combination of ZDV plus ddI or a triple combination of NVP plus ZDV plus ddI as a substudy of the AIDS Clinical Trials Group Protocol 241. Levels (approximating 3.5 determinations/patient) of the three drugs in plasma were measured during 44 of a total 48 weeks of study treatment, and a set of potential covariates was available for nonlinear mixed-effect modeling analysis. A one-compartment model with zero-order input and first-order elimination was fitted to the NVP data. Individual oral clearance (CL) and volume of distribution (V) averaged 0.0533 liters/h/kg of body weight and 1.17 liters/kg, respectively. Gender was the only covariate which significantly correlated with the CL of NVP. ZDV and ddI data were described by a two-compartment model with zero-order input and first-order elimination. Individual mean oral CL,V SS (volume of distribution at steady state), and V of ZDV were 1.84 liters/h/kg and 6.68 and 2.67 liters/kg, respectively, with body weight and age as correlates of CL and body weight as a correlate of V SS. The average individual oral CL, V SS, andV of ddI were 1.64 liters/h/kg and 3.56 and 2.74 liters/kg, respectively, with body weight as a significant correlate of both CL and V SS. The relative bioavailability (F) of ZDV and ddI in the triple combination compared to that in the double combination was also evaluated. No significant effects of the combination regimens on the F of ddI were detected (F TRIPLE = 1.05 andF DOUBLE = 1 by definition), but theF of ZDV was markedly reduced by the triple combination, being only 67.7% of that of the double combination. Large (>50%) intraindividual variability was associated with both ZDV and ddI pharmacokinetics. Individual cumulative area under the plasma drug level-time curve of the three drugs was calculated for the entire study period as a measure of drug exposure based on the individual data and the final-model estimates of structural and statistical parameters.

Zalcitabine Population Pharmacokinetics: Application of Radioimmunoassay

1998 ◽  
Vol 42 (2) ◽  
pp. 409-413 ◽  
Author(s):  
John M. Adams ◽  
Mark J. Shelton ◽  
Ross G. Hewitt ◽  
Mary DeRemer ◽  
Robin DiFrancesco ◽  
...  
Keyword(s):  
Population Pharmacokinetics ◽  
Information Age ◽  
Compartment Model ◽  
Volume Of Distribution ◽  
Pharmacokinetic Parameters ◽  
Pharmacokinetic Studies ◽  
Oral Clearance ◽  
Standard Curve ◽  
Immunodeficiency Virus ◽  
Traditional Approaches

ABSTRACT Zalcitabine population pharmacokinetics were evaluated in 44 human immunodeficiency virus-infected patients (39 males and 5 females) in our immunodeficiency clinic. Eighty-one blood samples were collected during routine clinic visits for the measurement of plasma zalcitabine concentrations by radioimmunoassay (1.84 ± 1.24 samples/patient; range, 1 to 6 samples/patient). These data, along with dosing information, age (38.6 ± 7.13 years), sex, weight (79.1 ± 15.0 kg), and estimated creatinine clearance (89.1 ± 21.5 ml/min), were entered into NONMEM to obtain population estimates for zalcitabine pharmacokinetic parameters (4). The standard curve of the radioimmunoassay ranged from 0.5 to 50.0 ng/ml. The observed concentrations of zalcitabine in plasma ranged from 2.01 to 8.57 ng/ml following the administration of doses of either 0.375 or 0.75 mg. A one-compartment model best fit the data. The addition of patient covariates did not improve the basic fit of the model to the data. Oral clearance was determined to be 14.8 liters/h (0.19 liter/h/kg; coefficient of variation [CV] = 23.8%), while the volume of distribution was estimated to be 87.6 liters (1.18 liters/kg; CV = 54.0%). We were also able to obtain individual estimates of oral clearance (range, 8.05 to 19.8 liters/h; 0.11 to 0.30 liter/h/kg) and volume of distribution (range, 49.2 to 161 liters; 0.43 to 1.92 liters/kg) of zalcitabine in these patients with the POSTHOC option in NONMEM. Our value for oral clearance agrees well with other estimates of oral clearance from traditional pharmacokinetic studies of zalcitabine and suggests that population methods may be a reasonable alternative to these traditional approaches for obtaining information on the disposition of zalcitabine.

scholarly journals Didanosine Population Pharmacokinetics in West African Human Immunodeficiency Virus-Infected Children Administered Once-Daily Tablets in Relation to Efficacy after One Year of Treatment

2009 ◽  
Vol 53 (10) ◽  
pp. 4399-4406 ◽  
Author(s):  
Déborah Hirt ◽  
Christophe Bardin ◽  
Serge Diagbouga ◽  
Boubacar Nacro ◽  
Hervé Hien ◽  
...  
Keyword(s):  
Human Immunodeficiency Virus ◽  
Viral Load ◽  
Compartment Model ◽  
Volume Of Distribution ◽  
Wilcoxon Test ◽  
Population Pharmacokinetic ◽  
Time Curve ◽  
Drug Concentrations ◽  
Immunodeficiency Virus ◽  
One Year

ABSTRACT Our objective was to study didanosine pharmacokinetics in children after the administration of tablets, the only formulation available in Burkina Faso for which data are missing, and to establish relationships between doses, plasma drug concentrations, and treatment effects (efficacy/toxicity). Didanosine concentrations were measured for 40 children after 2 weeks and for 9 children after 2 to 5 months of treatment with a didanosine-lamivudine-efavirenz combination. A population pharmacokinetic model was developed with NONMEM. The link between the maximal concentration of the drug in plasma (C max), the area under the concentration-time curve (AUC), and the decrease in human immunodeficiency virus (HIV) type 1 RNA levels after 12 months of treatment was evaluated. The threshold AUC that improved efficacy was determined by the use of a Wilcoxon test for HIV RNA, and an optimized dosing schedule was simulated. Didanosine pharmacokinetics was best described by a one-compartment model with first-order absorption and elimination. The apparent clearance and volume of distribution were higher for tablets, probably due to a lower bioavailability with tablets than with pediatric powder. The decrease in the viral load after 12 months of treatment was significantly correlated with the didanosine AUC and C max (P ≤ 0.02) during the first weeks of treatment. An AUC of >0.60 mg/liter·h was significantly linked to a greater decrease in the viral load (a decrease of 3 log10 versus 2.4 log10 copies/ml; P = 0.03) than that with a lower AUC. A didanosine dose of 360 mg/m2 administered as tablets should be a more appropriate dose than 240 mg/m2 to improve efficacy for these children. However, data on adverse events with this dosage are missing.

scholarly journals Population pharmacokinetics of dapsone administered biweekly to human immunodeficiency virus-infected patients.

1996 ◽  
Vol 40 (12) ◽  
pp. 2743-2748 ◽  
Author(s):  
G Gatti ◽  
M Merighi ◽  
J Hossein ◽  
S Travaini ◽  
R Casazza ◽  
...  
Keyword(s):  
Human Immunodeficiency Virus ◽  
Population Pharmacokinetics ◽  
Pneumocystis Carinii ◽  
Volume Of Distribution ◽  
Pharmacokinetic Parameters ◽  
Mixed Effect ◽  
Nonlinear Mixed Effect ◽  
Immunodeficiency Virus ◽  
Nonlinear Mixed Effect Modeling ◽  
Post Hoc

The population pharmacokinetics of dapsone were examined in human immunodeficiency virus-infected patients receiving dapsone at a dosage of 100 mg twice weekly for the prevention of Pneumocystis carinii pneumonia. Nonlinear mixed-effect modeling was used to determine the best pharmacostatistical model for the data. A one-compartment open model with first-order absorption and elimination was used as the structural pharmacokinetic model. Several covariates were tested for their influence on pharmacokinetic parameters. Rifampin was found to increase the values of clearance/bioavailability (CL/F) and volume of distribution/ bioavailability (V/F) by approximately 70%. CL/F and V/F were 1.83 liters/h and 69.6 liters, respectively, for patients not taking rifampin. The effect of rifampin on the pharmacokinetic parameters of dapsone was appreciably less than expected on the basis of studies with healthy volunteers. Increased bilirubin levels were associated with a significant decrease in the absorption rate constant (Ka). However, this finding may be considered clinically irrelevant because the post hoc Bayesian estimates of Ka for patients with high bilirubin levels ( > 1.2 mg/dl) were at the lower bound of the values for patients with normal bilirubin levels. The value of Ka was 0.957 h-1 for a patient with a bilirubin level of 0.7 mg/dl. After inclusion of covariates in the model, the interpatient variability was 35% for CL/F, not significant for V/F, and 85% for Ka. Simulation of plasma concentration-versus-time curves indicated that the administration of 100 mg of dapsone biweekly is associated with sustained dapsone levels in the plasma of the majority of the patients. Dosage adjustments for patients concomitantly treated with rifampin may be necessary.

Flat-Dosing Versus BSA-Based Dosing for MLN9708, An Investigational Proteasome Inhibitor: Population Pharmacokinetic (PK) Analysis of Pooled Data From 4 Phase-1 Studies

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 1433-1433 ◽  
Author(s):  
Neeraj Gupta ◽  
Mohammad Saleh ◽  
Karthik Venkatakrishnan
Keyword(s):  
Body Weight ◽  
Phase 1 ◽  
Compartment Model ◽  
Volume Of Distribution ◽  
Time Profile ◽  
Oral Dosing ◽  
First Order ◽  
Investigational Agent ◽  
Concentration Time ◽  
Population Pk

Abstract Abstract 1433 Background: Investigational agent MLN9708 is a potent, reversible and specific 20S proteasome inhibitor. Both intravenous (IV) and oral administration are being studied on a twice-weekly (Days 1, 4, 8, and 11; 21-day cycles) and weekly (Days 1, 8, and 15; 28-day cycles) schedule. The twice-weekly doses studied are 0.125–2.34 mg/m2 for IV and 0.24–2.23 mg/m2 for oral dosing. Weekly doses tested are 0.125–1.4 mg/m2 for IV and 0.24–3.95 mg/m2 for oral dosing. MLN9708 completely hydrolyzes to the pharmacologically active MLN2238 in aqueous solutions. Here we report a population PK analysis of pts with solid tumors, lymphoma or multiple myeloma (MM) enrolled in 4 ongoing phase 1 studies of IV and oral dosing on a twice-weekly (Days 1, 4, 8, 11; 21-day cycle) and weekly (Days 1, 8, 15; 28-day cycle) schedule. Methods: MLN9708 dose was based on body surface area (BSA) for both twice-weekly and weekly dosing schedules in solid tumor, lymphoma and MM patients (N=85). MLN2238 concentration-time data were analyzed using a non-linear mixed effects modeling approach (NONMEM® VII), with Intel® Visual Fortran Compiler, and the output was processed with SPLUS v8.1. Compartmental PK models were coded using the ADVAN 12 subroutine of NONMEM. A log-transform both sides approach was used. Estimation was by the First Order Conditional Estimation (FOCE) method with eta-epsilon interaction. Covariates tested included body weight, BSA, age, sex, dose and albumin on both clearance (CL) and volume, while creatinine clearance (CrCl), bilirubin, AST and ALT were only tested on CL parameters. Model validation and robustness were assessed using bootstrap simulations (N=1000) and visual predictive checks (N=100). Results: Mean age of 85 pts was 60.7 years, mean body weight was 80.0 kg, 87% of pts were Caucasian, and 58% were male. MLN9708 population PK was described by a three-compartment model with first order elimination. All model parameters were estimated with adequate precision when IV and oral data were fitted together. Of all the covariates tested, only body size descriptors (body weight and BSA) were found to be a significant covariate only on peripheral volume of distribution, V3 (p<0.01). Since BSA was more significant than body weight it was kept in the final model. Mean [%CV] CL (1.86 [7.0] L/h) and central volume of distribution (V2, 11.7 [13.1] L) were not affected by body weight or BSA. Inter-individual variability (IIV) was approximately 45% for CL, 82% for V2 and 30% for peripheral volume of distribution, with 17% of IIV in V3 explained by BSA. Absolute bioavailability (F) was estimated to be 62% based on this analysis. Based on simulations using the final population PK model, there was no difference in concentration-time profile or exposures (AUC or Cmax) between the BSA-based and the flat doses. Conclusions: Population PK analysis showed that the plasma concentration-time profile of MLN2238 can be well described by a three-compartment model with first order elimination process. Body size did not significantly impact AUC or Cmax, supporting a switch from BSA-based dosing to flat dosing in all ongoing and planned clinical studies. Ability to use a flat dosing paradigm may be a benefit for oral administration of MLN9708 due to its potential to simplify clinical management. Disclosures: Gupta: Millennium Pharmaceuticals, Inc.: Employment. Off Label Use: Investigational agent in clinical development for the treatment of solid tumors, lymphoma and MM. Saleh:Millennium Pharmaceuticals, Inc.: Student internship. Venkatakrishnan:Millennium Pharmaceuticals, Inc.: Employment.

scholarly journals Population Pharmacokinetics and Pharmacogenetics of Ethambutol in Adult Patients Coinfected with Tuberculosis and HIV

2019 ◽  
Vol 64 (2) ◽  
Author(s):  
Jesper Sundell ◽  
Emile Bienvenu ◽  
Sofia Birgersson ◽  
Angela Äbelö ◽  
Michael Ashton
Keyword(s):  
Body Weight ◽  
Population Pharmacokinetics ◽  
Treatment Guidelines ◽  
Plasma Concentrations ◽  
Relative Bioavailability ◽  
Volume Of Distribution ◽  
Current Treatment ◽  
Adult Patients ◽  
Fixed Dose ◽  
First Order

ABSTRACT This study aimed to characterize the population pharmacokinetics and pharmacogenetics of ethambutol in tuberculosis-HIV-coinfected adult patients. Ethambutol plasma concentrations, determined by liquid chromatography-tandem mass spectrometry, in 63 patients receiving ethambutol as part of rifampin-based fixed-dose combination therapy for tuberculosis were analyzed using nonlinear mixed-effects modeling. A one-compartment disposition model with first-order elimination and four transit compartments prior to first-order absorption was found to adequately describe the concentration-time profiles of ethambutol in plasma. Body weight was implemented as an allometric function on the clearance and volume parameters. Estimates of oral clearance and volume of distribution were 77.4 liters/h and 76.2 liters, respectively. A G/A mutation with regard to CYP1A2 2159 G>A was associated with a 50% reduction in relative bioavailability. Simulations revealed that doses of 30 mg/kg of body weight and 50 mg/kg for G/G and G/A carriers, respectively, would result in clinically adequate exposure. The results presented here suggest that CYP1A2 polymorphism affects ethambutol exposure in this population and that current treatment guidelines may result in underexposure in patients coinfected with tuberculosis and HIV. Based on simulations, a dose increase from15 to 20 mg/kg to 30 mg/kg is suggested. However, the 50-mg/kg dose required to reach therapeutic exposure in G/A carriers may be inappropriate due to the dose-dependent toxicity of ethambutol. Additional studies are required to further investigate CYP450 polymorphism effects on ethambutol pharmacokinetics.

Alteration in the Proportion of CD4 T Lymphocytes in a Subgroup of Human Immunodeficiency Virus-Exposed-Uninfected Children

PEDIATRICS ◽  
1994 ◽  
Vol 93 (4) ◽  
pp. 624-630
Author(s):  
Matthew Gesner ◽  
Vana Papaevangelou ◽  
Song-He Chen ◽  
Tiina Moore ◽  
Keith Krasinski ◽  
...  
Keyword(s):  
Human Immunodeficiency Virus ◽  
Statistical Significance ◽  
Weighted Average ◽  
Rate Of Change ◽  
Entire Study ◽  
Age Related ◽  
Wilcoxon Rank Sum Test ◽  
Immunodeficiency Virus ◽  
Cd4 Lymphocyte ◽  
Cd4 Percentage

Objective. The age-related changes in the proportion of CD4 and CD8 lymphocytes in human immunodeficiency virus (HIV)-seronegative children born to HIV-infected mothers (seroreverters) were compared with the changes in these lymphocyte subsets in children born to seronegative women to assess a possible effect of exposure to HIV without infection. Design. There were 146 seroreverter and 72 seronegative children. The median CD4 and CD8 percentages for each of these two groups of children were compared retrospectively at 3-month intervals from birth through 27 months and at a tenth interval for the time beyond 27 months. The weighted average of the within-subject rate of change of CD4 and CD8 percentages were also compared between the two groups. Finally, for each subject, the proportion of the subject's CD4 percentage assays which were &lt;10th percentile of the entire study population (30%) was calculated, and the distributions of the subject-specific proportions were then compared between the seronegative and seroreverter groups using the Wilcoxon rank sum test. The proportion of CD8 assays &lt;10th percentile (12%) or &gt;90th percentile (26%) were also computed for each subject, and the distributions of the proportions were compared similarily. Results. The median CD4 percentage for seroreverter children was lower than that for the seronegative children at every interval from birth through 27 months and for the last interval for values obtained at greater than 27 months, although the comparison was statistically significant only at the 4- to 6-month period. The weighted average of the within-subject rate of change of CD4 percentage was -0.09 and -3.0 per year (P .04), and of CD8 percentage was 1.3 and 1.0 (P = .67), for the seroreverter and seronegative children, respectively. There were significantly more children in the seroreverter group than in the seronegative group who had repeated assays in which the CD4 percentage was &lt;10th percentile for age (P &lt;.00005). In addition, there was a subset of 10 seroreverter children (6.8%) who had CD4 percentages &lt;30% on &gt;50% of their assays, as compared with only one (1.4%) seronegative child. The proportion of CD8 assays &lt;10th percentile or &gt;90th percentile were not significantly different between the two groups of children. Conclusions. The CD4 proportions were persistently lower in the seroreverter than in the seronegative population, although only reaching statistical significance in 1 of 10 3-month intervals. This finding may be due to a subgroup of seroreverter children who have persistently low CD4 lymphocyte percentages.

scholarly journals Pharmacokinetics of Stavudine and Didanosine Coadministered with Nelfinavir in Human Immunodeficiency Virus-Exposed Neonates

2001 ◽  
Vol 45 (12) ◽  
pp. 3585-3590 ◽  
Author(s):  
Chokechai Rongkavilit ◽  
Pimolrat Thaithumyanon ◽  
Theshinee Chuenyam ◽  
Bharat D. Damle ◽  
Sompop Limpongsanurak ◽  
...  
Keyword(s):  
Human Immunodeficiency Virus ◽  
Body Weight ◽  
Once Daily ◽  
Concentration Time ◽  
Pediatric Dose ◽  
Immunodeficiency Virus ◽  
To Receive

ABSTRACT We evaluated the pharmacokinetics of stavudine (d4T) and didanosine (ddI) in neonates. Eight neonates born to human immunodeficiency virus-infected mothers were enrolled to receive 1 mg of d4T per kg of body weight twice daily and 100 mg of ddI per m2 once daily in combination with nelfinavir for 4 weeks after birth. Pharmacokinetic evaluations were performed at 14 and 28 days of age. For d4T, on days 14 and 28, the median areas under the concentration-time curves from 0 to 12 h (AUC0–12s) were 1,866 and 1,603, ng · h/ml, respectively, and the median peak concentrations (C maxs) were 463 and 507 ng/ml, respectively. For ddI, on days 14 and 28, the median AUC0–10s were 1,573 and 1,562 h · ng/ml, respectively, and the median C maxs were 627 and 687 ng/ml, respectively. Systemic levels of exposure to d4T were comparable to those seen in children, suggesting that the pediatric dose of 1 mg/kg twice daily is appropriate for neonates at 2 to 4 weeks of age. Levels of exposure to ddI were modestly higher than those seen in children. Whether this observation warrants a reduction of the ddI dose in neonates is unclear.

scholarly journals Is the Recommended Dose of Efavirenz Optimal in Young West African Human Immunodeficiency Virus-Infected Children?

2009 ◽  
Vol 53 (10) ◽  
pp. 4407-4413 ◽  
Author(s):  
Déborah Hirt ◽  
Saik Urien ◽  
Mathieu Olivier ◽  
Hélène Peyrière ◽  
Boubacar Nacro ◽  
...  
Keyword(s):  
Human Immunodeficiency Virus ◽  
Body Weight ◽  
Plasma Concentrations ◽  
Individual Characteristics ◽  
Population Pharmacokinetic ◽  
Ratio Test ◽  
Time Curve ◽  
Once Daily ◽  
Concentration Time ◽  
Immunodeficiency Virus

ABSTRACT We aimed in this study to describe efavirenz concentration-time courses in treatment-naïve children after once-daily administration to study the effects of age and body weight on efavirenz pharmacokinetics and to test relationships between doses, plasma concentrations, and efficacy. For this purpose, efavirenz concentrations in 48 children were measured after 2 weeks of didanosine-lamivudine-efavirenz treatment, and samples were available for 9/48 children between months 2 and 5 of treatment. Efavirenz concentrations in 200 plasma specimens were measured using a validated high-performance liquid chromatography method. A population pharmacokinetic model was developed with NONMEM. The influence of individual characteristics was tested using a likelihood ratio test. The estimated minimal and maximal concentrations of efavirenz in plasma (C min and C max, respectively) and the area under the concentration-time curve (AUC) were correlated to the decrease in human immunodeficiency virus type 1 RNA levels after 3 months of treatment. The threshold C min (and AUC) that improved efficacy was determined. The target minimal concentration of 4 mg/liter was considered for toxicity. An optimized dosing schedule that would place the highest percentage of children in the interval of effective and nontoxic concentrations was simulated. The pharmacokinetics of efavirenz was best described by a one-compartment model with first-order absorption and elimination. The mean apparent clearance and volume of distribution for efavirenz were 0.211 liter/h/kg and 4.48 liters/kg, respectively. Clearance decreased significantly with age. When the recommended doses were given to 46 of the 48 children, 19% (44% of children weighing less than 15 kg) had C mins below 1 mg/liter. A significantly higher percentage of children with C mins of >1.1 mg/liter or AUCs of >51 mg/liter·h than of children with lower values had viral load decreases greater than 2 log10 copies/ml after 3 months of treatment. Therefore, to optimize the percentage of children with C mins between 1.1 and 4 mg/liter, children should receive the following once-daily efavirenz doses: 25 mg/kg of body weight from 2 to 6 years, 15 mg/kg from 6 to 10 years, and 10 mg/kg from 10 to 15 years. These assumptions should be prospectively confirmed.

scholarly journals Bayesian Parameter Estimates of Nelfinavir and Its Active Metabolite, Hydroxy-tert-Butylamide, in Infants Perinatally Infected with Human Immunodeficiency Virus Type 1

2005 ◽  
Vol 49 (2) ◽  
pp. 525-535 ◽  
Author(s):  
Salomé Payen ◽  
Albert Faye ◽  
Alexandra Compagnucci ◽  
Carlo Giaquinto ◽  
Diana Gibbs ◽  
...  
Keyword(s):  
Human Immunodeficiency Virus ◽  
Body Weight ◽  
Human Immunodeficiency Virus Type ◽  
Active Metabolite ◽  
Population Pharmacokinetic Model ◽  
Pharmacokinetic Model ◽  
Population Pharmacokinetic ◽  
Parameter Estimates ◽  
Immunodeficiency Virus

ABSTRACT The objective of the present study was to develop a population pharmacokinetic model for nelfinavir mesylate (NFV) and nelfinavir hydroxy-tert-butylamide (M8), the most abundant metabolite of NFV, in infants vertically infected with human immunodeficiency virus type 1 and participating in the Paediatric European Network for Treatment of AIDS 7 study. Plasma NFV concentrations were determined during repeated NFV administrations (two to three times a day). Eighteen infants younger that age 2 years participated in this study. The doses administered ranged from 71 to 203 mg/kg of body weight/day. Pharmacokinetic parameter estimates were obtained by a compartmental approach by using a kinetic model to simultaneously fit NFV and M8 (active metabolite) concentrations. M8 was shown to be formation rate limited and was characterized by first-order rate constants of formation and elimination. Body weight was found to be a more appropriate predictor than age of the changes in (i) the rate of metabolism, (ii) the elimination rate constant of NFV, and (iii) NFV clearance. Population parameters were computed to account for the relationship between the rate of metabolism and body weight. The estimated NFV and M8 elimination half-lives were 4.3 and 2.04 h, respectively. The estimated NFV clearance was 2.13 liters/h/kg. The M8 concentration-to-NFV concentration ratio was 0.64 ± 0.44. In conclusion, the population pharmacokinetic model describing the dispositions of NFV and M8 should facilitate the design of future studies to elucidate the relative contributions of the parent compound and M8 to the pharmacological and toxic effects of NFV therapy.

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