Efavirenz metabolism and CNS toxicity in Ugandan children: impact of CYP2B6 genotype and plasma metabolite profiles

Introduction: The non-nucleoside reverse transcriptase inhibitor efavirenz (EFV) is used in antiretroviral therapy (ART) against HIV. EFV is mainly metabolized by CYP2B6 to 8-hydroxyefavirenz (8-OH-EFV) and to a lesser extent by CYP2A6 to 7-hydroxyefavirenz (7-OH-EFV). Previous studies have only examined these metabolites in adults, indicating that EFV-hydroxy-metabolites might contribute to central nervous system (CNS) toxicity. Aims: This study aimed to quantify EFV and its metabolites including a recently identified EFV metabolite named EFAdeg in plasma and to explore their association with CYP2B6 metabolizer phenotypes and CNS adverse effects, in Ugandan children. Additionally, we examined signs of EFV autoinduction. Methods: ((8-OH-EFV + EFAdeg)/EFV) as the outcome variable. Results: Metabolite/EFV ratios in plasma varied significantly with CYP2B6 metabolizer phenotypes. Conjugated 8-OH-EFV (8-OH-EFV -glucuronide and 8-OH-EFV-sulfate) and conjugated EFAdeg constituted the major circulating forms of EFV in extensive and intermediate metabolizers, while the parent drug EFV dominated in slow metabolizers, who also displayed the highest levels of 7-OH-EFV. CNS symptoms were common, transient and mild and significantly associated with EFV plasma concentrations above 4,000 ng/mL and slow CYP2B6 metabolizer phenotype. None of the metabolites in plasma were associated with an increased risk of CNS toxicity. Evidence of autoinduction of EFV metabolism was observed among extensive metabolizers. Conclusion: This first study of EFV metabolites in children revealed distinct distribution patterns influenced by CYP2B6 metabolizer phenotype. Mild CNS-related adverse effects were associated with high EFV levels and slow CYP2B6 metabolizer phenotype, but not with EFV hydroxy metabolites. Autoinduction of EFV metabolism was observed in CYP2B6 extensive metabolizers.