Contribution of N-glucuronidation to efavirenz elimination in vivo in the basal and rifampin-induced metabolism of efavirenz

Doo Yeoun Cho, Evan T. Ogburn, David Jones, Zeruesenay Desta

Research output: Contribution to journalArticlepeer-review

28 Scopus citations


In this study, the contribution of efavirenz N-glucuronidation to efavirenz elimination in vivo was assessed. In a two-period placebo-controlled crossover trial design, a single 600-mg oral dose of efavirenz was administered to healthy volunteers (n = 10) pretreated with placebo pills or 600 mg/day rifampin orally for 10 days. Urine and plasma concentrations of efavirenz and 8-hydroxyefavirenz were measured by the liquid chromatography-tandem mass spectrometry method after enzymatic hydrolysis with β-glucuronidase (conjugated and unconjugated) and without enzymatic hydrolysis (unconjugated). Pharmacokinetic parameters of efavirenz within the placebo- or rifampin-treated group obtained after enzymatic hydrolysis did not show any statistically significant difference compared with those obtained without enzymatic hydrolysis (P > 0.05; paired t test, two-tailed). The amount of efavirenz excreted over 12 h was significantly larger after enzymatic hydrolysis in both the placebo (P = 0.007) and rifampin (P = 0.0001) treatment groups, supporting the occurrence of direct N-glucuronidation of efavirenz, but the relevance of this finding is limited because the amount of efavirenz excreted as unchanged or conjugated in urine is less than 1% of the dose administered. In both the placeboand rifampin-treated groups, plasma concentrations of 8-hydroxyefavirenz and the amount excreted over 12 h were significantly larger (P < 0.00001) after enzymatic hydrolysis than without enzymatic hydrolysis. These findings suggest that although the occurrence of direct efavirenz N-glucuronidation is supported by the urine data, the abundance of efavirenz N-glucuronide in plasma is negligible and that the contribution of the N-glucuronidation pathway to the overall clearance of efavirenz seems minimal.

Original languageEnglish (US)
Pages (from-to)1504-1509
Number of pages6
JournalAntimicrobial Agents and Chemotherapy
Issue number4
StatePublished - Apr 2011

ASJC Scopus subject areas

  • Pharmacology
  • Pharmacology (medical)
  • Infectious Diseases

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