Mechanism of ritonavir changes in methadone pharmacokinetics and pharmacodynamics: I. Evidence against CYP3A mediation of methadone clearance.

Published

Journal Article

Ritonavir diminishes methadone plasma concentrations, an effect attributed to CYP3A induction, but the actual mechanisms are unknown. We determined ritonavir effects on stereoselective methadone pharmacokinetics and clinical effects (pupillary miosis) in healthy human immunodeficiency virus-negative volunteers. Subjects received intravenous plus oral (deuterium-labeled) racemic methadone after no ritonavir, short-term (3-day) ritonavir, and steady-state ritonavir. Acute and steady-state ritonavir, respectively, caused 1.5- and 2-fold induction of systemic and apparent oral R- and S-methadone clearances. Ritonavir increased renal clearance 40-50%, and stereoselectively (S > R) increased hepatic methadone N-demethylation 50-80%, extraction twofold, and clearance twofold. Bioavailability was unchanged despite significant inhibition of intestinal P-glycoprotein. Intestinal and hepatic CYP3A was inhibited > 70%. Ritonavir shifted methadone plasma concentration-miosis curves leftward and upward. Rapid ritonavir induction of methadone clearance results from increased renal clearance and induced hepatic metabolism. Induction of methadone metabolism occurred despite profound CYP3A inhibition, suggesting no role for CYP3A in clinical methadone metabolism and clearance. Ritonavir may alter methadone pharmacodynamics.

Full Text

Duke Authors

Cited Authors

  • Kharasch, ED; Bedynek, PS; Park, S; Whittington, D; Walker, A; Hoffer, C

Published Date

  • October 2008

Published In

Volume / Issue

  • 84 / 4

Start / End Page

  • 497 - 505

PubMed ID

  • 19238655

Pubmed Central ID

  • 19238655

International Standard Serial Number (ISSN)

  • 0009-9236

Digital Object Identifier (DOI)

  • 10.1038/clpt.2008.104

Language

  • eng

Conference Location

  • United States