Promising HIV Strategy Falls Short

A large-scale study of a promising drug strategy to prevent HIV infection came to an abrupt end this week when an interim analysis revealed no difference between the experimental and control groups.

The study, which began in July 2009 and involved nearly 2000 women in South Africa, Tanzania, and Kenya who were at high risk of HIV infection, tested whether daily use of Truvada, a pill that contains two antiretroviral drugs, could thwart transmission via heterosexual sex. Given last year's celebrated finding that such pre-exposure prophylaxis (PrEP) stymies the virus in men who have sex with men, many expected this so-called FEM-PrEP study to succeed. An earlier study of one of the compounds in Truvada mixed with a vaginal gel had also found that it could prevent transmission when applied topically.

FHI, a nonprofit organization based in Durham, North Carolina, formerly known as Family Health International, ran FEM-PrEP and pulled the plug after independent observers determined the trial would not have the statistical power to demonstrate Truvada's effectiveness even if it were completed. FHI's Timothy Mastro, vice president for health and development sciences, suspects the "surprising and disappointing" results could be due to a combination of the drug not reaching the vaginal tissue and women not taking pills correctly.

In all, 56 women became infected during the study, half of whom received the drug and half a placebo. Women in the Truvada arm of the trial reported taking their pills 95% of the time, but earlier trials that analyzed blood levels of the drug have found great discrepancies with self reports. Mastro says the researchers have stored blood samples from participants and plan to assess drug levels.

Two other large studies of PrEP in women are under way in sub-Saharan Africa and will continue. Mitchell Warren, head of the AIDS Vaccine Advocacy Coalition in New York City, urges people not to extrapolate from the FEM-PrEP results. "It must be seen for what it is: the closure of a single trial in a field that has generated exciting results in the past," he says.