Evaluation of theophylline pharmacokinetics in a pediatric population using mixed effects models

Routine clinical pharmacokinetic data collected prospectively from pediatric patients receiving theophylline were analyzed using the NONMEM (nonlinear mixed effects model) digital computer program. A total of 314 measured serum theophylline concentrations (STCs) were obtained from 84 hospitalized patients ranging in age from 4 months to 15.2 years with the majority of patients between the ages of 1 and 8 years. Fifty-six percent were male. The race/ethnicity distribution was 71.4% Latin, 15.5% black, 11.9% Caucasian, and 1.2% (one subject) Pakistani. Of the total number of observed STCs, 16.2% reflected some degree of outpatient dosing. The pharmacokinetic model used was a one-compartment open model with either zero-order or first-order absorption and first-order elimination. Age was the most important determinant of theophylline clearance (Cl); weight was inferior to age and did not statistically improve the model (p greater than 0.005) when combined with age. Total Cl increased by 10%/year over the age range of 1 to 15 years of age. Black race and male gender were associated with higher Cl values: for a given age, Cl was 34% higher for blacks than the reference population composed of the remaining patients, and Cl for males was 25% higher than that for females. The volume of distribution (Vd) for the population was estimated to be 0.62 L/kg. The interindividual variability in Cl and Vd expressed as coefficients of variation were 19 and 28%, respectively. The residual intraindividual error variance corresponded to a standard deviation of 2.8 micrograms/ml. The STCs that represented some degree of outpatient dosing were 21% lower than those reflecting only inpatient dosing. Alternate models that include weight as a determinant of theophylline clearance are also provided. The NONMEM method of determining population pharmacokinetics is well suited to the pediatric population since it does not require a large number of STCs per patient. In this study a mean of only 3.7 STCs per patient were utilized to provide information which should prove useful in the design and adjustment of theophylline dosage regimens in children.     

住院病人茶碱群体药物动力学NONMEM法分析

对72名临床病人进行茶碱群体药物动力学研究,用NONMEM法分析了多种因素对茶碱药物动力学过程的影响。结果表明:在18至77a范围内,年龄对清除率(Cl)有显著性影响,每岁降低1.25％;长期多剂量服用茶碱的哮喘患者,Cl降低26.8％;OLD时Cl降低33.9％;合并用Ac-SPM时Cl略有降低,但影响不大;性别和体重对Cl无显著影响。     

A three-step approach combining bayesian regression and NONMEM population analysis: Application to midazolam

NONMEM, the only available supported program for population pharmacokinetic analysis, does not provide the analyst with individual subject parameter estimates. As a result, the relationship between pharmacokinetic parameters and demographic factors such as age, gender, and body weight cannot be sought by plotting demographic factors vs. kinetic parameters. To overcome this problem, we devised a three-step approach. In step 1, an initial NONMEM analysis provides the population pharmacokinetic parameters without taking into account the demographic factors. Step 2 consists of individual bayesian regressions using the measured drug concentrations for each subject and the population pharmacokinetic parameters obtained in step 1. The bayesian parameter estimates of the individual subject can be plotted against the demographic factors of interest. From the scatter plots, it can be seen which are the demographic factors that appear to affect the pharmacokinetic parameters. In step 3, the NONMEM analysis is resumed, and the demographic factors found in step 2 are entered into the NONMEM regression model in a stepwise manner. This method was used to analyze the pharmacokinetics of midazolam in 64 subjects from 714 plasma concentrations and 11 demographic factors. CL (elimination clearance) and V₁ were found to be a function of body weight. Age and liver disease were found to decrease CL. Of the 11 demographic factors recorded for each patient, none was found to influence V_ss or intercompartmental clearance.Supported in part by the Swiss National Science Foundation (Dr. Maitre) and the National Institute on Aging Grant R01-AG03104 (Dr. Stanski). Presented in abstract form at the Annual Meeting of the American Society for Clinical Pharmacology and Therapeutics, Nashville, TN, March 1989.     

Postinduction carbamazepine clearance in an adult psychiatric population

The objective of this study was to describe the postinduction clearance of carbamazepine (CBZ) in adult psychiatric patients by population pharmacokinetic analysis using the NONMEM program. Specifically, an estimate of CBZ clearance and insight into the effect of common patient characteristics on clearance were sought. Steady-state trough CBZ serum concentrations, CBZ dosing history, concomitant drug administration, and other data from 45 patients were collected retrospectively. A one-compartment model with first-order absorption and first-order elimination was used, with absorption rate, bioavailability, and volume of distribution fixed to literature values. No evidence was found that race, sex, age, ethanol use, smoking, and concomitant lithium significantly affected CBZ clearance. In the final model, clearance was based on lean body weight. The coefficient of variation for clearance estimates was 16.5%. Residual variability was modest. Estimates for volume of distribution, rates of absorption and elimination, and bioavailability could not be pursued rigorously. Although these results may assist in understanding CBZ disposition in this population, their general clinical application should be approached with caution.     

Population pharmacokinetics of zileution,a selective 5-lipoxygenase inhibitor,in patients with rheumatoid arthritis

The pharmacokinetics of zileuton, a novel selective 5-lipoxygenase inhibitor, were studied in 37 patients with rheumatoid arthritis after administration of 200 mg, 400 mg, and 600 mg zileuton for 4 weeks. Patients had 6-h pharmacokinetic evaluation of zileuton on day 14. Plasma zileuton concentrations were quantitated using HPLC. Zileuton pharmacokinetic parameters were estimated using standard noncompartmental methods. A population analysis of zileuton pharmacokinetics was also performed with the NONMEM computer program. The pharmacokinetics of zileuton in patients with rheumatoid arthritis were similar to those previously estimated in normal healthy humans. The peak concentrations and the areas under the curves during the dosing interval were dose proportional. The noncompartmental means of the CL/f, terminal-phase half-life, and V/f of zileuton were approximately 545 ml min^–1, 1.4 h, and 64.3 1, respectively. The estimate of population typical values of the CL/f for a 70-kg person (540 ml min^–1) and V/f for a 70-kg person (64.8 1) from the NONMEM analysis were in agreement with the noncompartmental estimates. Differences in body weight, but not age or gender, helped explain some of the variability in the pharmacokinetics of zileuton in patients. Therefore, there is no pharmacokinetic basis for alteration of the zileuton dose size or the dosing schedule in patients with rheumatoid arthritis.     

The population pharmacokinetics of theophylline in neonates and young infants

The population pharmacokinetics of theophylline were evaluated using 391 theophylline serum concentration measurements from 108 neonates and young infants (postnatal age 0–26 weeks), who received theophylline for the treatment of neonatal apnea. A one-compartment pharmacokinetic model with first-order elimination was used, with intravenous aminophylline and oral theophylline administration modeled as zero-order infusions. The effect of a variety of developmental and demographic factors on clearance (CL) and volume (V) were investigated. Hypothesis testing to evaluate potentially significant factors produced a final model in which clearance was based on weight (kg) raised to an exponential power and postnatal age (weeks), with CL (ml/hr)=17.5 (weight)^1.28 + 1.17 (postnatal age). Clearance was reduced by 12% for patients receiving parenteral nutrition. Volume of distribution in this population was adequately described using only weight, with V (L)=0.858 L/kg. Bioavailability of orally administered drug was not significantly less than unity. Interindividual variability in clearance was modest, with a coefficient of variation for clearance of 16%. An estimate of interindividual variability in volume could not be obtained. As a measure of residual variability in theophylline serum concentrations, the coefficients of variation for theophylline serum concentrations of 5.0, 10.0, and 13.0 mg/L were found to be approximately, 25, 12, and 9%, respectively. The identification of influential patient factors and the quantification of their influence on theophylline disposition allow for a priori estimates of theophylline pharmacokinetic parameters in these patients.This project was supported in part by a National Institutes of Health General Research Center grant 5MOI-RR00042.     

Population pharmacokinetics of lamotrigine adjunctive therapy in adults with epilepsy

Plasma concentrations of lamotrigine, an antiepileptic drug obtained in three adult controlled clinical trials conducted in the United States were pooled and analyzed using NONMEM, a population pharmacokinetic computer program, to facilitate development of dosing guidelines. A total of 2,407 lamotrigine plasma concentrations from 527 patients with epilepsy were analyzed. Regression equations for oral clearance were developed as a function of body size, age (18-64 years), gender, race, and use of concomitant antiepileptic drugs. The population mean apparent oral clearance of lamotrigine in adult patients receiving one concomitant enzyme-inducing antiepileptic drug and not valproic acid was estimated to be 1 mL/min/kg. Gender and age did not affect clearance significantly. On average, clearance was reduced by 25% in non-whites and increased by 13% in patients receiving more than one concomitant enzyme-inducing antiepileptic agent. Lamotrigine did not influence the disposition of phenytoin or carbamazepine. Dosing adjustments for lamotrigine in patients receiving concomitant enzyme-inducing antiepileptic drugs and not valproic acid should not be necessary for age, gender, or the number of concomitant enzyme-inducing antiepileptic drugs. Lamotrigine does not influence the dosing requirements for phenytoin or carbamazepine.     

NONMEM and NPEM2 population modeling: a comparison using tobramycin data in neonates

Nonlinear mixed effects modeling (NONMEM) and nonparametric expectation maximization (NPEM2) have both been used in population modeling of tobramycin. We compared both methods for differences in population pharmacokinetic parameters in relation to error models used. Predictive performance was compared between models. A group of 470 neonates who had received tobramycin according to a gestational age (GA)-dependent dosing interval was analyzed according to a one-compartment model with NONMEM and NPEM2. Additional models were constructed where the assay error pattern in NPEM2 mimicked NONMEM residual error and vice versa. Individual pharmacokinetic parameter estimates were compared. Predictive performance was evaluated in a separate group of 61 patients. Population estimates and variation coefficients (CV) for optimal models were NONMEM K(el) 0.071 h(-1) (27%), V(d) 0.59 L/kg (9%); NPEM2 K(el) 0.079 h(-1) (42%), V(d) 0.65 L/kg (48%). Forcing NONMEM to use the NPEM2 error pattern as residual error or vice versa resulted in smaller differences in CVs of the estimates. NONMEM gave less bias (P < 0.05) than NPEM2 and comparable precision with this approach. In conclusion NONMEM and NPEM2 are dissimilar in population estimates. Differences in ranges of pharmacokinetic parameter estimates between NONMEM and NPEM2 are largely determined by the method of incorporating error patterns in both programs.     

口服多剂量茶碱个体化给药方案的改良设计

目的:基于Excel表格程序设计茶碱个体化给药方案。方法:茶碱具有一室模型一级消除特征,根据群体药动学参数和患者个体的病理生理状态,设计个体化给药方案。结果:只需输入患者的年龄、身高、体重和病理生理状态及初始给药剂量和给药间隔,通过逻辑判断,程序即可自动快速计算出相应的稳态血药浓度值,通过改变给药剂量和给药间隔,观察稳态血药浓度变化范围,直至给药方案可行;也可求解任一时间点血药浓度。结论:根据茶碱群体药动学参数和患者的病理生理特点,可利用Excel表格程序设计茶碱个体化给药方案,方法简单、可靠、直观、易学。     

Population kinetics of tobramycin in neonates

The population kinetics of tobramycin were studied in 140 neonates (100/40 patients for the index/validation groups, respectively) of 30 to 42 weeks' gestational age and 0.8 to 4.25 kg current body weight in their first 2 weeks of life, undergoing routine therapeutic drug monitoring of their tobramycin serum levels. The 365 tobramycin concentration measurements obtained were analyzed by use of NONMEM according to a one-compartment open model with zero-order absorption and first-order elimination. The effect of a variety of demographic, developmental, and clinical factors (gender, height, birth weight, current weight, gestational age, postnatal age, postconceptional age, and serum creatinine concentration) on clearance and volume of distribution was investigated. Forward selection and backward elimination regression identified significant covariates. The final pharmacostatistical model with influential covariates was as follows (full population): clearance (L/h) = 0.0508 x current weight (kg), multiplied by 0.843 if birth weight was 2.5 kg or less (low-birthweight infants), and volume of distribution (L) = 0.533 x current weight (kg). Using the proportional error model for the random-effects parameters, interindividual variability for clearance and for volume of distribution was determined to be 25.8% and 21.9%, respectively, and the residual variability was 19.2%. In this study, the use of the NONMEM gave significant and consistent information on the pharmacokinetics and the determinants of the pharmacokinetic variability of tobramycin in neonates when compared with available bibliographic information. Moreover, the final population pharmacokinetic model may be used to design a priori recommendations for tobramycin and to improve the dosing readjustments through Bayesian estimation.     

Factors influencing the population pharmacokinetic parameters of phenytoin in adult epileptic patients in South Africa

The influence of various covariates (including weight, race, smoking, gender, age, mild-to-moderate alcohol intake, and body surface area) on the population pharmacokinetic parameters of phenytoin in adult epileptic patients in South Africa was investigated. The parameters were the maximum metabolic rate (Vm) and the Michaelis-Menten (MM) constant (Km) of phenytoin. The study population comprised 332 black and colored epileptic patients (note: "black" refers to indigenous people of South Africa, who speak one of the Bantu languages as their native language; "colored" refers to people considered to be of mixed race, classified as such by the apartheid former government of South Africa). The influence of covariates on Vm and Km estimates was determined using nonlinear mixed-effects modeling (NONMEM). Parameter models describing the factors that could potentially influence Vm and Km were tested using the Michaelis-Menten parallel MM and first-order elimination models, to which 853 steady state dose-to-serum concentration pairs were fitted. The results indicated that body weight, smoking, race, and age (65 years or older), in descending order of importance, significantly influenced Vm (p < 0.05). Although a significant difference (p = 0.03) in Km was found between black and colored patients, incorporating the influence of race in Km in the final regression model did not improve the fit of the model to the data, which indicated that the variability in Km was accounted for by Vm. The scaling factors for smoking, colored patients and age (65 years or older) in Vm were 1.16, 1.10, and 0.88, respectively. These factors should be taken into account when adjusting phenytoin dose.     

Digoxin population pharmacokinetics from routine clinical data: role of patient characteristics for estimating dosing regimens.

Routine clinical pharmacokinetic data collected from patients receiving digoxin have been analysed to evaluate the role of patient characteristics for estimating dosing regimens. The data were analysed using NONMEM, a computer program designed for population pharmacokinetic analysis that allows pooling of data. The pharmacokinetic model of digoxin was described using a one-compartment steady-state model. The effect of a variety of developmental and demographic factors on clearance was investigated. NONMEM estimates indicate that digoxin clearance was influenced by the demographic variables of age, total body weight, serum creatinine and sex. The interindividual variability in digoxin clearance was modelled with additive error with an estimated standard deviation of 46.15 L day-1 and the intraindividual variability, or residual error was 0.209 ng mL-1. The dosing method based on clearance values obtained by NONMEM analysis allowed the prediction of the steady-state concentration as a function of maintenance dose with acceptable error for therapeutic drug monitoring.     

Population pharmacokinetics of free carbamazepine in adult Omani epileptic patients

OBJECTIVE: The aim of this study was to define the pharmacokinetic profile of free carbamazepine (F-CBZ) in adult Omani epileptic patients in order to improve on dosing schedules through population pharmacokinetic analysis using the NONMEM program. METHOD: Steady-state trough F-CBZ serum concentrations, carbamazepine (CBZ) dosing history and associated information were collected prospectively. RESULTS: Forty-eight patients with two or more available F-CBZ serum concentrations (total of 149 dose/serum concentration pairs) met our inclusion criteria. Patients were taking CBZ (200-1200 mg/day) in monotherapy. The analysis assumed a one-compartmental open model with first-order absorption and elimination. The apparent clearance (CL/F) and apparent volume of distribution (V/F) and their interindividual variabilities were estimated using the program. The population estimates for clearance (CL; modelled independently of dose) and volume of distribution were 13.2 +/- 0.6 l/h and 525 +/- 44 1, respectively. However, CL increased as a function of dosing rate and consequently was modelled as a linear function of steady-state concentration. In order to validate these results, the predictions of the population model were tested against data from 13 further patients subjected to the same inclusion criteria but who were not included in the original analysis. The predictions were good, being unbiased (P=0.31), and had an average deviation from the observed values of 18%. CONCLUSION: In order to establish steady-state dosage regimens, a population pharmacokinetic model is proposed, based on the patient's dose, to estimate the individual CL for an Omani epileptic patient receiving CBZ in monotherapy.     

Population pharmacokinetics of lamotrigine monotherapy in patients with epilepsy: retrospective analysis of routine monitoring data

Aims To examine the population pharmacokinetics of lamotrigine in patients newly diagnosed with epilepsy and receiving oral lamotrigine monotherapy for up to 48 weeks.
Methods The population consisted of 158 Caucasians and 5 Asians of whom 81 were males and 82 females. Age and weight ranged between 14 and 76 years and 41–107  kg, respectively. A one-compartment compartment model with first-order absorption and elimination was fitted to plasma lamotrigine concentration-time profiles from retrospective drug monitoring, using non-linear mixed effect modelling (NONMEM), with first-order estimation. Oral clearance (CL_o ), apparent volume of distribution ( V  / F ) and absorption rate constant ( K _a ) were the main pharmacokinetic parameters.
Results CL_o was not significantly influenced by body weight, age, gender, oral contraceptives and dose. However, due to auto-induction CL_o increased by 17.3% during the 48 weeks of therapy, from 1.94 to 2.28  l h⁻¹, and was 28.7% lower in Asians than Caucasian. The final magnitude in interpatient variability was 32%. The effect of the covariates weight, age, race and gender on V  / F was examined and none was statistically significant. The final population estimate of V  / F was 77.4  l with an interpatient variability of 34%.
Conclusions In view of the wide therapeutic margin of lamotrigine and the 21% residual variability in plasma concentrations, the modest significant effects of race and auto-induction on clearance are unlikely to be clinically significant and, thus, no dosage adjustment is warranted for these effects.     

Population pharmacokinetic analysis of two theophylline formulations in premature neonates and infants with apnea

A study was conducted to clarify differences in the theophylline pharmacokinetics of two orally available products, theophylline alcohol and Apnecut, in premature neonates and infants using population pharmacokinetic analysis. Fifty-two patients with apnea hospitalized at the National Center for Child Health and Development were enrolled (total number of plasma concentration points=90). Population pharmacokinetic analysis under steady-state conditions was performed using NONMEM ver. V. The mean oral clearance was 0.0249 (l/h), and the inter- and intraindividual variation was 30.3% and 28.3%, respectively, in the basic model. The oral clearance was significantly affected by body weight, sex, and age. The final model obtained was expressed by the following equation: oral clearance (l/h)=0.0201 x (body weight (g)/1000)(1.08)x (1-0.282 x drug product), where theophylline alcohol is 0 and Apnecut is 1. The inter- and intraindividual variations in the final model were 15.0% and 15.3%, respectively. The oral clearance of the two oral formulations differed significantly, and this difference should be considered when adjusting the theophylline dose.     

茶碱在老年慢性阻塞性肺疾病患者中的群体药动学

目的：建立茶碱在老年慢性阻塞性肺疾病患者中的群体药动学（PPK）模型,并获取药动学参数,为临床制定个体化给药方案提供参考。方法：收集2014年4—12月某院诊断为慢性阻塞性肺疾病应用茶碱治疗的68例老年患者的血药浓度监测数据及临床资料,运用非线性混合效应模型法（NONMEN）定量分析性别、年龄、体质量及肝肾功能等因素对药动学参数的影响,最终建立PPK模型。采用拟合优度、自举法和可视化检验对最终模型的性能进行内部验证。结果：茶碱的药动学符合一室模型,最终模型公式为：CL=θ_CL×（WT/63）^θWT×exp（η_CL）,V=θ_V×exp（η_V）,其中的协变量为体质量,模型CL和V的群体典型值分别为0.849 L·h^-1,13.7 L。拟合优度、自举法和可视化检验的评价结果表明最终模型稳定,预测结果可靠。结论：建立的PPK模型能较好地描述茶碱在老年慢性阻塞性肺疾病患者中的药动学特点,患者体质量对参数CL有显著性影响。     

The effects of erythromycin on the absorption and disposition kinetics of theophylline

Summary The effects of erythromycin on the kinetics of theophylline were investigated in eight female patients with documented asthma in a crossover study. Theophylline pharmacokinetics were determined at steady state before and after one-week treatment with erythromycin stearate 250 mg given four times a day. Multiple serum samples were collected for 12 h after an aminophylline dose in the two drug treatment phases and assayed by high performance liquid chromatography. The resultant serum theophylline concentration-time data were analyzed by weighted, nonlinear regression analysis to obtain various pharmacokinetic parameters. In this study, the elimination half-live increased from 7.8±1.7 h on the control day to 9.5±1.4 h following treatment with the antibiotic (p<0.02). The estimated apparent volume of distribution for theophylline (V/F) was also observed to increase from 0.42±0.09 l/kg before treatment with erythromycin to 0.53±0.15 l/kg after antibiotic treatment (0.05<p<0.10). In this study, no difference was demonstrated in the apparent clearance rate (Cl_app), apparent first-order absorption rate constant (k_a), maximum serum drug concentration (C_max), time of maximum drug concentration (T_max) or absorption lag time (t_lag) for theophylline before and after treatment with erythromycin. With no apparent alteration in theophylline clearance following erythromycin coadministration, the decrease in the first-order elimination rate constant suggested that the apparent volume of distribution of theophylline is increased in the presence of erythromycin. It is concluded that patients maintained on theophylline derivatives should be closely monitored when erythromycin is coadministered.     

Population pharmacokinetics of piperacillin/tazobactam in neonates and young infants

Objectives

To develop population pharmacokinetic (PK) models for piperacillin/tazobactam in neonates and infants of less than 2 months of age in order to determine the appropriate dosing regimen and provide a rational basis for the development of preliminary dosing guidelines suitable for this population.

Methods

A two-stage, open-label study was conducted in neonates and infants less than 2 months of age in the neonatal intensive care unit (NICU). A total of 207 piperacillin and 204 tazobactam concentration–time data sets from 71 patients were analyzed using a nonlinear mixed-effect modeling approach (NONMEM VII). PK models were developed for piperacillin and tazobactam. The final models were evaluated using both bootstrap and visual predictive checks. External model evaluations were made in 20 additional patients.

Results

For neonates and young infants less than 2 months of age, the median central clearance was 0.133 and 0.149 L/h/kg for piperacillin and tazobactam, respectively. Postmenstrual age (PMA) was identified as the most significant covariate on central clearance of piperacillin and tazobactam. However, the combination of current bodyweight (BW) and postnatal age proved to be superior to PMA alone. BW was the most important covariate for apparent central volume of distribution. Both internal and external evaluations supported the prediction of the final piperacillin and tazobactam PK models. The dosing strategy 44.44/5.56 mg/kg/dose piperacillin/tazobactam every 8 or 12 h evaluated in this study achieved the pharmacodynamic target (free piperacillin concentrations >4 mg/L for more than 50 % of the dosing interval) in about 67 % of infants.

Conclusions

Population PK models accurately described the PK profiles of piperacillin/tazobactam in infants less than 2 months of age. The results indicated that higher doses or more frequent dosing regimens may be required for controlling infection in this population in NICU.     

Population pharmacokinetics of peginterferon alfa-2b in pediatric patients with chronic hepatitis C

Purpose

The aim of this study was to characterize the population pharmacokinetics of peginterferon (PEG-IFN) alfa-2b in pediatric patients with chronic hepatitis C and to identify covariates influencing PEG-IFN alfa-2b disposition.

Methods

Pharmacokinetic data from a multicenter open-label study of subcutaneously administered peginterferon alfa-2b (60 μg/m²/wk) plus oral ribavirin (15 mg/kg/day) in patients with chronic hepatitis C aged 3–17 years old was used to develop a population pharmacokinetic nonlinear mixed-effects model.

Results

The final population pharmacokinetic analysis was conducted with the pooled data from 107 pediatric patients. A one-compartment model with first-order absorption, first-order elimination, exponential inter-individual variability on clearance, and a combination additive and proportional residual error model adequately described the PEG-IFN alfa-2b pharmacokinetic profile. Age (apparent clearance and apparent volume of distribution) and sex (apparent clearance) were significant covariates. The mean body surface area normalized apparent clearance of PEG-IFN alfa-2b was 0.56 L/h/m², and was similar when evaluated across the pediatric age groups.

Conclusion

The final population model suggests age-dependent increases in clearance and volume of distribution of PEG-IFN alfa-2b in pediatric patients with chronic hepatitis C. The apparent clearance normalized to body surface area was similar across pediatric age groups, supporting the use of body size–adjusted dosing in pediatric subjects.     

Development of a Population Pharmacokinetic Model for Taranabant, a Cannibinoid-1 Receptor Inverse Agonist

Taranabant is a cannabinoid-1 receptor inverse agonist developed for the treatment of obesity. A population model was constructed to facilitate the estimation of pharmacokinetic parameters and to identify the influence of selected covariates. Data from 12 phase 1 studies and one phase 2 study were pooled from subjects administered single and multiple oral doses of taranabant ranging from 0.5 to 8 mg. A total of 6,834 taranabant plasma concentrations from 187 healthy and 385 obese subjects were used to develop the population model in NONMEM. A standard covariate analysis using forward selection (α = 0.05) and backward elimination (α = 0.001) was conducted. A three-compartment model with first-order absorption and elimination adequately described plasma taranabant concentrations. The population mean estimates for apparent clearance and apparent steady-state volume of distribution were 25.4 L/h and 2,578 L, respectively. Statistically significant covariate effects were modest in magnitude and not considered clinically relevant (the effects of body mass index (BMI) and creatinine clearance (CrCL) on apparent clearance; BMI, age, CrCL, and gender on apparent volume of the peripheral compartment and age on apparent intercompartmental clearance). The pharmacokinetic profile of taranabant can adequately be described by a three-compartment model with first-order absorption and elimination. Clinical dose adjustment based on covariates effects is not warranted.Key words: NONMEM, obesity, pharmacokinetics, population, taranabant