A recently completed substudy of a larger clinical trial found that pre-exposure prophylaxis -- a new strategy to prevent HIV infection by prescribing a daily antiretroviral drug to at-risk individuals -- can be a powerful tool when participants take their medications. The trial of this strategy, also called PrEP, enrolled uninfected individuals in East Africa with an HIV-positive sexual partner and found that a combination of objective monitoring of how often participants took their daily medications and intensive counseling of those with lower rates of adherence prevented any HIV infection among those receiving active medication during an average follow-up period of nearly one year.
"Our study shows that PrEP can be extremely effective in preventing HIV infection when adherence to daily dosing is high," says Jessica Haberer, MD, MS, of the Center for Global Health at Massachusetts General Hospital (MGH), lead author of the article in the September 10 issue of PLOS Medicine. "Previous studies of PrEP have found considerable variance in efficacy, ranging from as high as 75 percent to no effect at all. We think that the different levels of adherence in those trials explain the differences in their findings, a hypothesis that is supported by this new study."
The larger Partners PrEP Study was conducted from July 2008 until July 2011 at nine clinical sites in Kenya and Uganda and enrolled almost 5,000 couples, one member of which was HIV-infected and the other was not. Uninfected participants were prescribed daily oral medications -- either one of two different antiretroviral formulations or a placebo. At the outset of the trial and at monthly intervals during the study period, both members of the couples received counseling on the importance of following the trial protocol, including consistently taking the study drug, and other ways to prevent HIV transmission.