Level 1: Likely reliable evidence

Postexposure HIV prophylaxis has been recommended for men who have sex with men, but the window to start treatment is short (72 hours) and evidence for its efficacy is limited.

The recent Pre-exposure Prophylaxis Initiative trial evaluated the safety and efficacy of a two-drug cocktail for HIV chronic prophylaxis in 2,499 men and transgender women who have sex with men. Participants—who were HIV-negative at baseline—were randomized to a combination of emtricitabine (Emtriva) and tenofovir (Viread) vs. placebo orally once daily and were followed for a median of 1.2 years. All participants received HIV testing, risk-reduction counseling, condoms, and management of sexually transmitted infections.

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HIV infection rates were significantly lower in the prophylaxis group (2.9% vs. 5.1%, P=0.005, NNT 46). There were no significant differences in overall or serious adverse events or in study-drug discontinuation. Of potential concern, chemoprophylaxis was associated with higher rates of unintended weight loss of more than 5% (2.2% vs. 1.1%, P=0.04, NNH 91). It was also associated with higher rates of nausea (1.6% vs. 0.7%,P=0.04, NNH 111). In a subgroup analysis of the chemoprophylaxis group, participants with detectable levels of the study drug had markedly decreased risk of HIV infection compared with those without detectable levels (relative risk reduction 92%, 95% CI 70%-99%).