**11. Microbicides for prevention of HIV transmission**

Recently, strategies for prevention of HIV-1 infection with topical formulations for vaginal application and/or rectal have been receiving attention. Whereas most phase I and phase II clinical trials have found microbicide compounds to be safe and well tolerated, phase III trials completed to date have not demonstrated efficacy in preventing HIV transmission [191]. Different topical microbicides under study for prevention of HIV-1 are grouped into classes of agents, based on where they disrupt the pathway of sexual transmission of HIV. These classes include surfactants/membrane disruptors, vaginal milieu protectors, viral entry inhibitors, reverse transcriptase inhibitors, and other groups whose mechanism is unknown. Surfactants and acidifying agents act non-specifically, either by disrupting viral and cellular membranes, or creating a more hostile environment in the genital tract for viral transmission [191-193] (Table 6).
