['Efavirenz, an antiretroviral medicine, is extensively metabolized by cytochrome P450 2B6 (CYP2B6), UDP-glucuronosyltransferase 2B7 (UGT2B7), and CYP2A6. In this study, we investigated the association of single nucleotide polymorphisms (SNPs) in these genes with plasma efavirenz levels in Zimbabwean human immunodeficiency virus (HIV)-positive patients treated with efavirenz.', 'The exon regions of the CYP2B6, CYP2A6, and UGT2B7 genes were re-sequenced in 49 HIV-infected Zimbabwean patients treated with a combination therapy including efavirenz. Associations of SNPs in these three genes with efavirenz plasma concentrations 11-16\xa0h after the administration of treatment were evaluated.', 'Eight patients carrying CYP2B6*6/*18 showed the highest plasma efavirenz levels, with a fourfold higher concentration than patients who carried CYP2B6*1/*1. Patients with CYP2B6*6/*6 also showed higher efavirenz plasma concentrations than those with CYP2B6*1/*1. Among the 17 and 12 SNPs identified in CYP2A6 and UGT2B7, respectively, no SNP showed a significant association with the plasma efavirenz concentration.'] Is cYP2B6 genotype a strong predictor of systemic exposure to efavirenz in HIV-infected Zimbabweans?