Population Approach to Efavirenz Therapy.

Efavirenz (EFV) is a nonnucleoside reverse transcriptase inhibitor commonly used as first-line therapy in the treatment of human immunodeficiency virus (HIV), with a narrow therapeutic range and a high between-subject variability which can lead to central nervous system toxicity or therapeutic failure. To characterize the sources of variability and better predict EFV steady-state plasma concentrations, a population pharmacokinetic model was developed from 96 HIV-positive individuals, using a nonlinear mixed-effect method with Monolix® software. A one-compartment with first-order absorption and elimination model adequately described the data. To explain between-subject variability, demographic characteristics, biochemical parameters, hepatitis C virus-HIV coinfection, and genetic polymorphisms were tested. A combination of the single-nucleotide polymorphisms rs2279343 and rs3745274, both in the CYP2B6 gene, were the only covariates influencing clearance, included in the final model. Oral clearance was estimated to be 19.6 L/h, 14.15 L/h, and 6.08 L/h for wild-type, heterozygous mutated and homozygous mutated individuals, respectively. These results are in accordance with the current knowledge of EFV metabolism and also suggest that in homozygous mutated individuals, a dose adjustment is necessary. Hepatitis C virus-HIV coinfection does not seem to be a predictive indicator of EFV pharmacokinetic disposition.