A Population Pharmacokinetic Analysis of Nelfinavir Mesylate in Human Immunodeficiency Virus-Infected Patients Enrolled in a Phase III Clinical Trial

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Abstract
A population pharmacokinetic analysis was conducted on nelfinavir in patients infected with human immunodeficiency virus (HIV) who were enrolled in a phase III clinical trial. The data consisted of 509 plasma concentrations from 174 patients who received nelfinavir at a dose of 500 or 750 mg three times a day. The analysis was performed using nonlinear mixed-effect modeling as implemented in NONMEM (version 4.0; double precision). A one-compartment model with first-order absorption best described the data. The timing and small number of early postdose blood levels did not allow accurate estimation of volume of distribution ( V/F ) and the absorption rate constant ( k a ). As a result, two models were used to analyze the data: model 1, in which oral clearance (CL/ F ), V/F , and k a were estimated, and model 2, in which V/F and k a were fixed to known values and only CL/ F was estimated. Estimates of CL/ F ranged from 41.9 to 45.1 liters/h, values in close agreement with previous studies. Neither body weight, age, sex, race, dose level, baseline viral load, metabolite-to-parent drug plasma concentration ratio, history of liver disease, nor elevated results of liver function tests appeared to be significant covariates for clearance. The only significant covariate-parameter relationship was concomitant use of fluconazole on CL/ F , which was associated with a modest reduction in interindividual variability of CL/ F . Patients who received concomitant therapy with fluconazole had a statistically significant reduction in nelfinavir CL/ F of 26 to 30%. Since serious dose-limiting toxicity and concentration-related toxicities are not apparent for nelfinavir, this effect of fluconazole is unlikely to be of clinical significance.