Emtricitabine: A novel nucleoside reverse transcriptase inhibitor

Abstract

Emtricitabine is a once-daily nucleoside reverse transcriptase inhibitor (NRTI) that selectively and potently inhibits human immunodeficiency virus type 1 (HIV-1) replication. Emtricitabine is used in combination with other antiviral agents for the treatment of HIV-1 and is currently under investigation for the treatment of hepatitis B virus (HBV) infection. Like other NRTIs, emtricitabine is activated to a triphosphate derivative, which mediates the antiviral effect. Emtricitabine triphosphate is incorporated into a primer DNA strand resulting in chain termination and blockade of DNA- or RNA-directed DNA synthesis. One key benefit of emtricitabine over other NRTIs is its favorable pharmacokinetic profile that permits once-daily dosing; it has a long mean plasma elimination half-life of 8-10 hours, and the intracellular half-life of emtricitabine triphosphate is 39 hours after multiple doses of 200 mg daily. In adult patients infected with HIV-1, emtricitabine has a convenient and simple dosing schedule of one 200-mg capsule once daily, and is as effective as lamivudine 150 mg twice daily and more effective than stavudine twice daily at suppressing plasma HIV-1 RNA when administered as part of a triple-drug regimen. Also, triple therapy including emtricitabine is as effective as a protease inhibitor- based regimen in maintaining durable suppression of plasma HIV-1 RNA levels in adults. Early clinical results show that triple therapy including emtricitabine is also effective in decreasing or maintaining durable suppression of HIV-1 RNA levels in children and adolescents with HIV-1 infection. It is also effective against HBV in patients co-infected with HIV-1 and in patients monoinfected with HBV. In clinical practice, emtricitabine is generally very well tolerated, with most adverse events being mild to moderate in severity. The now available combination of emtricitabine with tenofovir in the same pill makes it a very attractive backbone combination to use in conjunction with other antiretroviral drugs.