Objective: To determine the safety and effectiveness of BufferGel and 0.5% PRO2000 microbicide gels for the prevention of male-to-female HIV transmission. Design: Phase II/IIb, randomized, placebo-controlled trial with three double-blinded gel arms and an open-label no gel arm. Methods: Study participants from Malawi, South Africa, Zambia, Zimbabwe, and the USA were instructed to apply study gel up to 1 h before each sex act and safety, sexual behavior, pregnancy, gel adherence, acceptability, and HIV serostatus were assessed during follow-up. Results: The 3101 enrolled women were followed for an average of 20.4 months with 93.6% retention and 81.1% self-reported gel adherence. Adverse event rates were similar in all study arms. HIV incidence rates in the 0.5% PRO2000 gel, BufferGel, placebo gel, and no gel arms were 2.70, 4.14, 3.91, and 4.02 per 100 women-years, respectively. HIV incidence in the 0.5% PRO2000 gel arm was lower than the placebo gel arm (hazard ratio = 0.7, P=0.10) and the no gel arm (hazard ratio = 0.67, P=0.06). HIV incidence rates were similar in the BufferGel and both placebo gel (hazard ratio =1.10, P=0.63) and no gel control arms (hazard ratio =1.05, P=0.78). HIV incidence was similar in the placebo gel and no gel arms (hazard ratio =0.97, P=0.89). Conclusion: The 0.5% PRO2000 gel demonstrated a modest 30% reduction in HIV acquisition in women. However, these results were not statistically significant and subsequent findings from the Microbicide Development Programme (MDP) 301 trial have confirmed that 0.5% PRO2000 gel has little or no protective effect. BufferGel did not alter the risk of HIV infection. Both products were well tolerated.

Results of the HPTN 035 trial. Abstract 48LB (16th Conference on Retroviruses and Opportunistic Infections, 2009).