Effect of Tenofovir Disoproxil Fumarate on the Pharmacokinetics and Pharmacodynamics of Total, R‐, and S‐Methadone

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Abstract
Study Objective. To evaluate the potential effect of tenofovir disoproxil fumarate (DF) on the pharmacokinetics of methadone.Design. Phase I, open‐label, fixed‐sequence, pharmacokinetic drug‐drug interaction study.Setting. Clinical research center.Subjects. Fourteen volunteers receiving stable methadone maintenance therapy who were not infected with the human immunodeficiency virus.Intervention. Tenofovir DF was added to the subjects' methadone regimens.Measurements and Main Results. The pharmacokinetics of total, R‐, and S‐methadone were evaluated at baseline and after 2 weeks of daily tenofovir DF coadministration with a light meal. Steady‐state tenofovir DF pharmacokinetics were evaluated at day 15. Bioequivalence testing was conducted of total, R‐, and S‐methadone area under the serum or plasma concentration‐time curve during the 24‐hour dosing interval at steady state (AUCss) and maximum concentration in serum or plasma (Cmax). Subjects were evaluated for changes in methadone pharmacodynamics by the Short Opiate Withdrawal Scale (SOWS) and pupillary diameter measurements at frequent intervals. Coadministration with tenofovir DF did not affect the pharmacokinetics of methadone. Geometric mean R‐methadone systemic exposures, AUCss and Cmax, differed by 5% or less when methadone was dosed with tenofovir D F. Similar results were observed for S‐methadone and for total methadone. Both AUCss and Cmax met the strict criteria for bioequivalence between the two study periods for total, R‐, and S‐methadone, indicating a lack of drug interaction when tenofovir DF was coadministered with methadone. No significant changes in SOWS scores or pupillary diameter measurements occurred, and no notable clinical adverse events were reported.Conclusion. Tenofovir DF pharmacokinetics were comparable to previously reported values of tenofovir DF in HIV‐infected patients. Coadministration of methadone with tenofovir DF did not alter the pharmacokinetics or pharmacodynamics of total, R‐, or S‐methadone. Tenofovir DF may be given as part of a once‐daily antiretroviral regimen in patients receiving methadone maintenance therapy.