November 12, 2010
Clinical trials testing biomedical means to prevent HIV infection during sex are gaining momentum, experts say.
Last year, a South African trial found that a tenofovir-based vaginal gel conferred about 40 percent protection against HIV. Even though only partially effective, it was the first method for preventing HIV that women could use without men knowing -- a vital need, since many males refuse to wear condoms. Other trials are expected to post results next year and in 2012. If successful, a market-ready product could be possible by 2013. In addition, gels could also protect against herpes.
In the coming months, "we're going to see a cascade of results" from trials of oral pre-exposure prophylaxis, said Mitchell Warren, executive director of AVAC, an HIV prevention advocacy group. In them, people in high-risk groups take one or two of the antiretroviral drugs typically prescribed to those already infected. It is hoped the ARVs will protect participants from sexually acquired HIV. Regulatory approval might be quick for oral PREP, since ARVs taken orally are already approved.
Rectal microbicides also are on the radar, though progress lags about 10 years behind the vaginal microbicide field, said Dr. Ian McGowan, who leads microbicide trials at the University of Pittsburgh. According to some surveys, 95 percent of U.S. men who have sex with men and 40 percent of heterosexual women have had anal sex at least once in their life.
However, it is first crucial to ensure the gels do not inflame the rectal lining, which is weaker than the vaginal lining. HIV targets activated immune cells, so a gel that inflamed tissue could enhance HIV infection. Tests will soon begin on less viscous formulations that do not pull as much water into the rectum, McGowan said. A 2008 British study in monkeys found a rectally applied tenofovir gel was very effective in preventing anal acquisition of simian immunodeficiency virus.