Taking Tenofovir PrEP in US Trial Not Tied to More Sexual Risk in MSM

US men who have sex with men (MSM) taking daily tenofovir for preexposure prophylaxis (PrEP) did not have more sex partners or more unprotected (condom-free) anal sex after they started PrEP. But men who believed PrEP prevents HIV acquisition had a slightly but significantly greater number of total partners after starting PrEP.

iPrEx, an international placebo-controlled trial, determined that daily PrEP with tenofovir/emtricitabine lowers the risk of HIV acquisition in MSM. The US trial focused on the safety of daily tenofovir alone versus placebo, and the impact of taking PrEP on sexual risk taking. Researchers randomized 373 healthy HIV-negative MSM in Atlanta, Boston, and San Francisco to immediate tenofovir, tenofovir delayed for 9 months, immediate placebo, or placebo delayed for 9 months. When the trial began and every 3 months, participants answered questions about sexual risk using Audio Computer-Assisted Self-Interview.

Overall rates of sexual risk taking fell or remained stable during the 24 months of study. Average number of partners and reports of unprotected anal sex fell significantly during follow-up (P < 0.05), while average number of anal sex acts without a condom remained the same.

During the first 9 months of the trial, sexual risk taking was similar in the group that began tenofovir or placebo immediately and in the group that delayed pill taking. Among men who delayed pill taking for 9 months, indicators of sexual risk did not change after they started taking pills. Nor did these indicates change after 9 months in men who started taking tenofovir or placebo immediately.

Men who believed PrEP would lower the risk HIV acquisition were slightly but significantly more likely to have more total partners than men who did not believe PrEP would be effective (incidence rate ratio 1.04, 95% confidence interval 1.00 to 1.08, P = 0.04).

Men who used poppers, amphetamines, or sexual performance-enhancing drugs were more likely to have more total partners, any unprotected anal sex, and/or more unprotected anal sex episodes than men who did not use these drugs.

"We found no evidence of risk compensation [taking more risks as a result of using a possibly preventive intervention] among at-risk MSM initiating PrEP in this trial," the researchers conclude. Still, they recommend monitoring for risk compensation in MSM using PrEP now that iPrEx has established the efficacy of daily tenofovir/emtricitabine PrEP in MSM.

The authors stress the importance of addressing substance use in MSM using or not using PrEP.

Source: Albert Y. Liu, Eric Vittinghoff, Kata Chillag, Kenneth Mayer, Melanie Thompson, Lisa Grohskopf, Grant Colfax, Sonal Pathak, Roman Gvetadze, Brandon O'Hara, Brandi Collins, Marta Ackers, Lynn Paxton, Susan P. Buchbinder. Sexual risk behavior among HIV-uninfected men who have sex with men participating in a tenofovir preexposure prophylaxis randomized trial in the United States. JAIDS. 2013; 64: 87-94.

Written by Mark Mascolini on behalf of the International AIDS Society