Taking HIV pre-exposure prophylaxis (PrEP) does not lead to increased levels of sexual risk behaviour among gay men, investigators from the United States report in the online edition of the Journal of Acquired Immune Deficiency Syndromes. Numbers of sexual partners fell, as did the proportion of men reporting unprotected anal sex.
“We found no evidence of risk compensation among at-risk MSM [men who have sex with men] initiating PrEP,” comment the authors. “Mean numbers of partners and the proportion of men reporting UAS [unprotected anal sex] decreased significantly from baseline during 24 months of follow-up.”
PrEP is an emerging HIV prevention technology. It involves HIV-negative individuals taking daily antiretroviral therapy to reduce their risk of infection with the virus. In 2010, results of the iPrEx trial involving gay and other MSM showed that daily PrEP with Truvada (FTC and tenofovir) reduced the risk of infection with HIV by 44% overall, with high efficacy seen in people with the best treatment adherence. Although the results of PrEP studies involving heterosexuals have been mixed, the United States Food and Drug Administration approved Truvada for use as PrEP by adults with a high risk of HIV infection.
However, there is concern in some quarters that use of PrEP may lead to increases in sexual risk behaviour. Mathematical models suggest that even modest increases in the proportion of gay men reporting unprotected sex could wipe out the beneficial effect of PrEP at a community level. However, the precise impact of PrEP on sexual risk taking is highly controversial.
Data gathered during a PrEP safety study allowed investigators to explore the impact of PrEP on the sexual risk behaviour of HIV-negative gay men with a high risk of infection with HIV.
A total of 400 men were recruited to the study between 2005 and 2007. All reported anal sex with another man in the preceding twelve months. The study was double blind and placebo controlled. Participants were randomised either to start treatment immediately or to wait for nine months. The men were interviewed at baseline and then every three months about their sexual risk behaviour and use of recreational and erectile dysfunction drugs. The study lasted 24 months.
At baseline, the men reported a mean of 7.25 sexual partners in the previous three months. This fell significantly during follow-up to a mean of 6 partners between months 3 and 9 and a mean of 5.71 partners between months 12 and 24 (p < 0.001). These declines were similar in the immediate- and delayed-treatment arms.
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