July 13, 2011 -- Drugs that suppress HIV in infected people may also help protect healthy people who take them from getting the virus through sexual contact, two new studies show.
The studies found that the antiretroviral medications, which can be given as once-daily pills, cut the infection risk by as much as 73% compared to a placebo.
The two studies were conducted in Africa among heterosexual couples, and they provide the first evidence that the strategy, which is called pre-exposure prophylaxis, may help both men and women.
Last year, an international trial showed the drugs could cut HIV transmission among men who have sex with men by as much as 90% among those who used them consistently.
Experts hailed the studies as a major milestone in the global effort to stop the AIDS epidemic.
"What a great day this truly is for HIV prevention," says study researcher Michael C. Thigpen, MD, a CDC epidemiologist, at a news conference. "Just a few years ago, we had very few tools" to prevent infection, he says.
Now in addition to male circumcision, condoms, and behavioral modifications, researchers say medications can also be used to reduce the risk of HIV transmission between intimate partners, though the CDC is still developing guidelines on how best to use the drugs.
"It's a breakthrough in prevention because it's an additional mechanism we have to try to tackle an HIV epidemic that's still growing in the world and in the United States," says Jonathan Mermin, MD, director of the division of HIV/AIDS prevention at the CDC.
Other experts agree.
"This is really a game changer," says study researcher Jared Baeten, MD, an associate professor of global health and medicine at the University of Washington in Seattle. "Now what we need is to get these strategies out to people so they'll have a large effect at populations with greatest need."
The first study, called The Partners PrEP Trial, has been following 4,758 couples, in which one member has HIV and the other does not, in Kenya and Uganda.
All couples were given intensive counseling about safer sex practices, contraceptives, condoms, and monitoring and treatment for STDs.
The couples were evenly divided into three groups: one took a daily placebo pill, the second got a daily dose of the drug tenofovir, and a third was assigned to a daily combination pill with the drugs tenofovir and emtricitabine, which is sold under the brand name Truvada.
After 36 months, 78 new HIV infections had occurred in the study. There were 18 in those taking tenofovir alone, 13 in those assigned to the combination pill, and 47 among those who were taking a placebo.
Those who were taking tenofovir alone had an average of 62% fewer HIV infections, while those who received the combination pill had 73% fewer infections than those on the placebo. The differences between the two groups were not statistically significant, meaning one regimen was not better than the other.