In this study the combination of nevirapine 200 mg twice daily with tenofovir DF 300 mg once daily and nevirapine 400 mg once daily with tenofovir DF 300 mg once daily were compared with nevirapine twice daily or once daily without tenofovir DF in HIV-infected patients.

In addition, the combination of efavirenz 600 mg and tenofovir DF 300 mg once daily was compared with use of efavirenz 600 mg once daily only.

Data were retrospectively collected from routine therapeutic drug monitoring plasma samples. Nevirapine, efavirenz, and tenofovir plasma levels and tenofovir concentration ratios were analyzed.

Six different groups were studied: 200 mg nevirapine twice daily, 400 mg nevirapine once daily, 600 mg efavirenz once daily, all without tenofovir DF (groups 1, 2, and 3, respectively), and the same groups with the drugs combined with tenofovir 300 mg once daily (groups 4, 5, and 6, respectively).

Results

Plasma samples were evaluable for 272, 18, 126, 32, 94, and 118 patients in the groups 1-6, respectively.

No differences were found in plasma levels for tenofovir, nevirapine, and efavirenz for either of the combinations studied.

Addition of tenofovir DF to efavirenz or nevirapine in HIV-infected patients does not influence the plasma levels of nevirapine or efavirenz.

Nevirapine and efavirenz have no effect on tenofovir plasma levels or tenofovir concentration ratios.

The authors conclude, “Efavirenz or nevirapine can be coadministered with tenofovir DF in HIV-infected patients without dose modifications.”

01/17/05

Reference
J A Droste and others. Assessment of Drug-Drug Interactions Between Tenofovir Disoproxil Fumarate and the Nonnucleoside Reverse Transcriptase Inhibitors Nevirapine and Efavirenz in HIV-Infected Patients. Journal of Acquired Immune Deficiency Syndrome 41(1): 37-43. January 1, 2006.

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