Pharmacokinetics of Plasma Efavirenz and CYP2B6 Polymorphism in Southern Chinese

Cytochrome P450 2B6 (CYP2B6) is the main metabolizing pathway for efavirenz (EFV), the prescription of which is associated with neurologic side effects. The authors conducted a study on the prevalence of CYP2B6 polymorphism, profile of side effects, and pharmacokinetics of EFV in a group of human immunodeficiency virus (HIV)-infected southern Chinese. Patients with HIV were recruited at the Shenzhen City Third People's Hospital, China. The prevalence of CYP2B6 G516T and plasma EFV concentration were determined. Pharmacokinetics was assessed using blood samples of selected patients at time 0, 1, 2, 4, 8, 12, and 24 hours after the last dose of EFV Between October 2007 and June 2008, 79 Chinese patients with HIV were recruited. Sequencing of CYP2B6 at position 516 gave 42 GG, 34 GT, and 3 TT genotypes, with corresponding mean spot plasma EFV level of 3.4, 4.1, and 8.1 mg/L, respectively. The allelic frequency of 516 G > T was 0.25. Univariate analysis showed that plasma EFV level correlated with genotype (P = 0.02). Eighteen patients completed the pharmacokinetic study: TT genotype gave the longest half-life (t(1/2)), highest plasma EFV concentration, and largest area under the curve. The volume of distribution per surface area (Vd(ss)), total clearance (Cltot), and elimination rate constant (ke) were the lowest. There was no association between the occurrence of side effects and the EFV concentration (chi(2) test, P > 0.05). The EFV pharmacokinetics of TT genotype differed significantly from GG and GT genotypes. Accumulation of EFV may potentially occur over time, causing toxicity in TT and GT genotypes.