A prophylactic medicine that preliminary research has suggested prevents HIV infection among gay men appears to have no effect on women.
Researchers stopped one in a series of long-term studies testing the antiretroviral drug Truvada on thousands of African women who are at high risk of HIV infection after preliminary data showed an equal HIV infection rate among both women who took Truvada and those who took a placebo.
Many experts say they found the results of the study, known as FEM-PrEP, disappointing, since Truvada is regarded as a groundbreaking drug for HIV prevention among gay men. Researchers believed Truvada would also work for high-risk women in Africa.
"We were surprised by the outcome," said Dr. Timothy Mastro, vice president of health and developmental science at FHI, the nongovernmental organization that oversaw the study. "We were advised that there was no benefit to continue for the next several months."
A number of possible reasons could have contributed to the findings, according to Mastro. One reason, according to the organization, could be that the women may not have been taking the medication as advised, if they were taking it at all. Or the medication might not work for women the way it seemed to work for men.
"The final data have not been confirmed," said Mastro. "So at this point, all we can say is that the study was not able to conclude that Truvada works for women."
The first study of the series, called iPrEx, which looked at Truvada, was published November 2010 in the New England Journal of Medicine. It offered the first indication of an oral method to prevent the spread of HIV among those at high risk.
"This is an important trial that further extends the growing appreciation that antiretroviral therapy can play a vital role in controlling the HIV epidemic," said Dr. Paul Volberding, co-director of the University of California at San Francisco Center for AIDS Research, who was not involved in the study.
The study, which began in June 2007, followed 2,499 men and transgender women from six countries -- including the United States -- who engaged in sex with other men and were categorized as high risk for HIV infection. Participants were randomized to either receive a combination antiretroviral drug known as Truvada or a placebo.
Participants assigned to Truvada who reported taking the daily pills about half of the time they were prescribed had about a 50 percent lower risk of getting HIV. Those who reported taking the medication about 90 percent of the time had a 73 percent lower risk of infection.
"We think our results can be generalized to all communities in the world," Dr. Javier Lama, a study co-chairman from Investigaciones Medicas en Salud in Peru, said at the time.
In 2008, more than 42,000 people in the U.S. were diagnosed with HIV. Nearly half of those infected were men who had sex with men, according to the Centers for Disease Control and Prevention.
According to Dr. Tom Coates, director of the UCLA program in global health, condom use "has already decreased due to HIV treatment being so effective.
"HIV prevention is already not working all that well among gay men," Coates said.