The experimental vaginal microbicide PRO 2000, which appeared promising in earlier studies, did not protect women from becoming infected with HIV in a large Phase III clinical trial in Africa, investigators announced in December.
PRO 2000 is a 0.5% microbicidal gel inserted into the vagina prior to sexual intercourse. An earlier study of more than 3,000 African women (HPTN 035) was the first to suggest that a microbicide might help prevent male-to-female sexual transmission of HIV, with a 30% protective effect that fell just short of statistical significance.
But the MDP 301 trial -- the largest microbicide study to date, with more than 9,000 participants -- found no evidence that PRO 2000 reduced women's risk of infection. Over 12-24 months of follow-up, the HIV incidence rate was 4.5 per 100 person-years in the PRO 2000 arm versus 4.3 per 100 person-years in the placebo arm.
Speaking at CROI, Fauci said that studies of non-antiretroviral microbicides like PRO 2000 have produced "failure after failure," and the time has come to move on to next-generation products containing antiretroviral agents such as tenofovir or maraviroc.
Liz Highleyman (email@example.com) is a freelance medical writer based in San Francisco.