First (Sort of) Positive Anti-HIV Microbicide Trial

First (Sort of) Positive Anti-HIV Microbicide Trial

Promising results from HPTN 035, a phase II trial of two microbicides, were reported at the 2009 Retrovirus Conference.

Several anti-HIV microbicide trials have been conducted in recent years, but none have yielded positive results . . . until now. At this year’s Retrovirus Conference, Salim Abdool Karim presented the much-awaited results of HPTN 035, a phase II/IIb trial designed to assess the safety and efficacy of two microbicides for the prevention of HIV infection in women [Abstract 48LB].

More than 3000 women from Malawi, South Africa, Zambia, Zimbabwe, and the U.S. were randomized to receive 0.5% PRO 2000 gel, BufferGel, placebo gel, or no gel. (PRO 2000 gel is a polyanionic polymer intended to bind to positive charges on the surface of HIV and prevent it from entering cells. BufferGel increases the natural acidity of the vagina.) The three gel arms were double blinded.

During an average follow-up of 20 months, gel adherence was 81% across the gel arms. Condom use was 72% in the gel arms and 81% in the no-gel arm. The rate of new HIV infection was 30% lower among PRO 2000 gel recipients than among women who received placebo gel or no gel, but this difference was not statistically significant in an intent-to-treat analysis. A post hoc analysis, stratified by adherence level, suggested that these results are not a fluke: Women who reported using PRO 2000 gel at least 85% of the time achieved a 44% reduction in infection risk, whereas those who used the gel less frequently achieved only a 9% reduction. BufferGel did not influence infection risk. Both active gels were found to be safe. A separate phase III study of PRO 2000 gel in more than 9000 women is ongoing, and those results are eagerly anticipated.

— Carlos del Rio, MD

Published in Journal Watch HIV/AIDS Clinical Care March 9, 2009

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