Effects of clopidogrel and itraconazole on the disposition of efavirenz and its hydroxyl metabolites: exploration of a novel CYP2B6 phenotyping index

Br J Clin Pharmacol. 2013 Jan;75(1):244-53. doi: 10.1111/j.1365-2125.2012.04314.x.


Aims: To evaluate the effects of clopidogrel and itraconazole on the disposition of efavirenz and its hydroxyl metabolites in relation to the CYP2B6*6 genotype and explore potential phenotyping indices for CYP2B6 activity in vivo using a low dose of oral efavirenz.

Methods: We conducted a randomized three phase crossover study in 17 healthy Korean subjects pre-genotyped for the CYP2B6*6 allele (CYP2B6*1/*1, n = 6; *1/*6, n = 6; *6/*6, n = 5). Subjects were pretreated with clopidogrel (75 mg day(-1) for 4 days), itraconazole (200 mg day(-1) for 6 days), or placebo and then given a single dose of efavirenz (200 mg). The plasma (0-120 h) and urine (0-24 h) concentrations of efavirenz and its metabolites (7- and 8-hydroxyefavirenz and 8,14-dihydroxyefavirenz) were determined by LC/MS/MS.

Results: This study is the first to delineate quantitatively the full (phase I and II) metabolic profile of efavirenz and its three hydroxyl metabolites in humans. Clopidogrel pretreatment markedly decreased AUC(0,48 h), C(max) and Ae(0,24 h) for 8,14-dihydroxyefavirenz, compared with placebo; 95% CI of the ratios were 0.55, 0.73, 0.30, 0.45 and 0.25, 0.47, respectively. The 8,14-dihydroxyefavirenz : efavirenz AUC(0,120 h) ratio was significantly correlated with the weight-adjusted CL/F of efavirenz (r(2) ≈ 0.4, P < 0.05), differed with CYP2B6*6 genotype and was affected by clopidogrel pretreatment (P < 0.05) but not by itraconazole pretreatment.

Conclusions: The disposition of 8,14-dihydroxy-EFV appears to be sensitive to CYP2B6 activity alterations in human subjects. The 8,14-dihydroxyefaviremz : efavirenz AUC(0,120 h) ratio is attractive as a candidate phenotyping index for CYP2B6 activity in vivo.

Publication types

  • Randomized Controlled Trial
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alkynes
  • Anti-HIV Agents / pharmacokinetics*
  • Antifungal Agents / pharmacology*
  • Aryl Hydrocarbon Hydroxylases / genetics*
  • Benzoxazines / pharmacokinetics*
  • Clopidogrel
  • Cross-Over Studies
  • Cyclopropanes
  • Cytochrome P-450 CYP2B6
  • Genotype
  • Humans
  • Hydroxylation
  • Itraconazole / pharmacology*
  • Male
  • Oxidoreductases, N-Demethylating / genetics*
  • Phenotype
  • Platelet Aggregation Inhibitors / pharmacology*
  • Ticlopidine / analogs & derivatives*
  • Ticlopidine / pharmacology


  • Alkynes
  • Anti-HIV Agents
  • Antifungal Agents
  • Benzoxazines
  • Cyclopropanes
  • Platelet Aggregation Inhibitors
  • Itraconazole
  • Clopidogrel
  • Aryl Hydrocarbon Hydroxylases
  • CYP2B6 protein, human
  • Cytochrome P-450 CYP2B6
  • Oxidoreductases, N-Demethylating
  • efavirenz
  • Ticlopidine