In vitro analysis and quantitative prediction of efavirenz inhibition of eight cytochrome P450 (CYP) enzymes: Major effects on CYPs 2B6, 2C8, 2C9 and 2C19

Research output: Contribution to journalArticle

33 Scopus citations


In order to quantitatively predict drug interactions associated with efavirenz-based anti-HIV therapy, we evaluated reversible and time-dependent inhibitions of efavirenz on eight cytochrome P450 (CYP) enzymes in vitro. The present study showed that efavirenz was a potent competitive inhibitor of CYP2B6 (average Ki = 1.68 μM in HLMs and Ki = 1.38 μM in expressed CYP2B6) and CYP2C8 (Ki = 4.78 μM in pooled HLMs and Ki = 4.80 μM in HLMs with CYP2C8*3/*3 genotype). Efavirenz was a moderate inhibitor of CYP2C9 (Ki = 19.46 μM) and CYP2C19 (Ki = 21.31 μM); and a weak inhibitor of CYP3A (Ki = 40.33 μM). No appreciable inhibition was observed on CYP1A2, CYP2A6 or CYP2D6. No time-dependent inhibition of the CYPs by efavirenz was observed in this study. Quantitative predictions showed that single dose of efavirenz may substantially slow the elimination of drugs predominately cleared by CYP2B6, CYP2C19 or by both enzymes and may also lower the area under the plasma concentration time curve (AUC) of active metabolites of some pro-drugs (e.g., clopidogrel and proguanil) by up to 30%. Depending on substrates, chronic administration of efavirenz may increase the AUC of CYP2C8 and CYP2C9 substrates about 3.5-4.4-fold and 1.7-2.0-fold at steady state.

Original languageEnglish (US)
Pages (from-to)362-371
Number of pages10
JournalDrug Metabolism and Pharmacokinetics
Issue number4
StatePublished - Aug 25 2013



  • Antiretroviral agents
  • Cytochrome P450
  • Drug-drug interaction
  • Quantitative prediction
  • Reversible inhibition
  • Time-dependent inhibition

ASJC Scopus subject areas

  • Pharmacology (medical)
  • Pharmacology
  • Pharmaceutical Science

Cite this