A vaginal gel form of the HIV drug tenofovir can reduce a woman's chances of being infected with the virus by a male sexual partner, the results of a South African clinical trial suggest.

"Tenofovir gel could fill an important HIV prevention gap by empowering women who are unable to successfully negotiate mutual faithfulness or condom use with their male partners," said Dr. Quarraisha Abdool Karim, co-principal investigator of the double-blind, randomized control trial, in a news release Monday.

Karim is associate director of the Centre for the AIDS Programme of Research in South Africa (CAPRISA) and associate professor of epidemiology at Columbia University in New York.

"This new technology has the potential to alter the course of the HIV epidemic, especially in southern Africa where young women bear the brunt of this devastating disease," Karim said.

The results need to be confirmed.

Results of the South African trial are being presented at the International AIDS Conference currently taking place in Vienna and appear in Monday's online issue of the journal Science.

For the trial, about 445 women received the tenofovir gel, and 444 received a placebo gel. The women were told to use it 12 hours before sex and as soon as possible within 12 hours afterward.

All participants were tested for HIV at monthly follow-up visits, at which they also received reproductive health services, such as pregnancy tests, and HIV prevention services, including pre- and post-test counseling, HIV risk-reduction counseling, condoms and treatment for other sexually transmitted infections.

Adherence questions

At the end of the study, there were 38 HIV infections among the microbicide group compared with 60 in the other group.

About 40 per cent of the women in the trial had below 50 per cent adherence, which points to a need to enhance and objectively measure how closely women followed instructions about using the gel, the study's authors said.

Mild diarrhea was slightly more common among those using the gel.

The effectiveness of the gel seemed to decline after 18 months, which needs to be investigated further, the researchers said.

The gel is not available commercially. It was made for this and another ongoing study by California-based Gilead Sciences Inc., which sells tenofovir as a pill.

Gilead has licensed the rights to produce the gel royalty-free in the world's 95 poorest countries, said Dr. Howard Jaffe, president of the Gilead Foundation, the company's philanthropic arm.

The study was sponsored by CAPRISA; Family Health International; CONRAD, an AIDS research effort based at Eastern Virginia Medical School; and the U.S. Agency for International Development, or USAID.

With files from The Associated Press