In vivo analysis of efavirenz metabolism in individuals with impaired CYP2A6 function

Pharmacogenet Genomics. 2009 Apr;19(4):300-9. doi: 10.1097/FPC.0b013e328328d577.


Introduction: The antiretroviral drug efavirenz (EFV) is extensively metabolized into three primary metabolites: 8-hydroxy-EFV, 7-hydroxy-EFV and N-glucuronide-EFV. There is a wide interindividual variability in EFV plasma exposure, explained to a great extent by cytochrome P450 2B6 (CYP2B6), the main isoenzyme responsible for EFV metabolism and involved in the major metabolic pathway (8-hydroxylation) and to a lesser extent in 7-hydroxylation. When CYP2B6 function is impaired, the relevance of CYP2A6, the main isoenzyme responsible for 7-hydroxylation may increase. We hypothesize that genetic variability in this gene may contribute to the particularly high, unexplained variability in EFV exposure in individuals with limited CYP2B6 function.

Methods: This study characterized CYP2A6 variation (14 alleles) in individuals (N=169) previously characterized for functional variants in CYP2B6 (18 alleles). Plasma concentrations of EFV and its primary metabolites (8-hydroxy-EFV, 7-hydroxy-EFV and N-glucuronide-EFV) were measured in different genetic backgrounds in vivo.

Results: The accessory metabolic pathway CYP2A6 has a critical role in limiting drug accumulation in individuals characterized as CYP2B6 slow metabolizers.

Conclusion: Dual CYP2B6 and CYP2A6 slow metabolism occurs at significant frequency in various human populations, leading to extremely high EFV exposure.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alkynes
  • Alleles
  • Anti-HIV Agents / blood
  • Anti-HIV Agents / chemistry
  • Anti-HIV Agents / metabolism*
  • Anti-HIV Agents / pharmacokinetics
  • Aryl Hydrocarbon Hydroxylases / metabolism*
  • Asian People / genetics
  • Benzoxazines / blood
  • Benzoxazines / chemistry
  • Benzoxazines / metabolism*
  • Benzoxazines / pharmacokinetics
  • Black People / genetics
  • Cyclopropanes
  • Cytochrome P-450 CYP2A6
  • Gene Frequency
  • Genetic Variation
  • Hispanic or Latino / genetics
  • Humans
  • Metabolic Networks and Pathways / genetics*
  • Molecular Structure
  • Pharmacogenetics*
  • Polymorphism, Single Nucleotide
  • White People / genetics


  • Alkynes
  • Anti-HIV Agents
  • Benzoxazines
  • Cyclopropanes
  • Aryl Hydrocarbon Hydroxylases
  • CYP2A6 protein, human
  • Cytochrome P-450 CYP2A6
  • efavirenz