Microbicides to prevent heterosexual transmission of HIV: ten years down the road.

The development of topical microbicides for HIV prevention originated in response to the unabated spread of HIV despite the availability of an effective HIV prevention tool (condoms), as well as the lack of an effective HIV vaccine. Initially, hopes were pinned on existing over-the-counter spermicides containing nonoxynol-9. Concern about the toxicity of nonoxynol-9 with frequent use, and its small or nonexistent protective effect against HIV and other sexually transmitted infections (STIs), has spurred the development of new microbicides with a number of novel mechanisms of action. Significant progress has been made in the last decade. The microbicides pipeline currently contains approximately 34 products in preclinical development, 15 in Phase I safety trials, four in Phase II expanded safety and preliminary effectiveness trials, and three in Phase II/III or Phase III effectiveness trials. Laboratory and clinical research has been complemented by a growing body of research and literature on microbicide acceptability, harm reduction and dual protection strategies, and potential markets. However, many challenges remain, including the need for a significant increase in investment to accelerate product development and complementary research, and to plan for availability and access once effective microbicides are available.