Vaginal microbicides may help prevent heterosexual HIV transmission


WESTPORT, CT (Reuters Health) – Animal studies indicate that two vaginal microbicides, dextrin-2-sulphate (D2S) and PRO-2000 (P2K), may provide a degree of protection again HIV infection, without undue toxicity.

Previous clinical studies have shown that nonoxynol-9 (N9) does not reduce HIV transmission when used as a vaginal virucide. In fact, the licensed spermicidal agent can cause inflammation and mucosal disruption that may actually promote transmission. D2S and P2K, however, have demonstrated anti-HIV activity in vitro, and phase I trial results suggest that they do not cause vaginal inflammation.

In a study reported in the August 17th issue of AIDS, Dr. Jonathan N. Weber, from the Imperial College School of Medicine in London, UK, and colleagues assessed the in vitro and in vivo activity of D2S, P2K, N9, and gramicidin-D (GD). The in vivo activity of the agents was evaluated in macaques that were vaginally challenged with SHIV, a hybrid of the simian and human immunodeficiency viruses.

The researchers found that all four agents inhibited SHIV in vitro. Three of the four macaques that did not receive an antiviral agent showed evidence of infection. Infection was confirmed in half of the macaques treated with P2K, D2S, or GD. One out of four macaques treated with N9 showed evidence of infection.

An additive antiretroviral effect of D2S with GD was noted in vitro, but all of the macaques treated with this combination therapy became infected.

"Although protection was incomplete in the macaque model, the natural challenge situation is difficult to simulate experimentally," the researchers state. "Vaginal agents with a 50% efficacy could have a significant effect on population rates of HIV acquisition," they add.

"In the context of irregular condom use, vaginal microbicides could halve the risk of HIV transmission per act of intercourse," the investigators note. "A combination of intermittent use of condoms, which effectively reduce the number of exposures, with vaginal agents that reduce the risk per exposure, is likely to exert an additive effect on the reduction of HIV transmission."

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