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."
Testing Medication to Prevent HIV
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.
Researchers reported having very high levels of medication adherence in their study, saying that more than 97% of dispensed pills were taken. That was determined by the number of pills that were returned to study investigators at monthly check-in visits. Researchers have also taken blood tests to confirm blood levels of the study medications, but those results have not yet been analyzed, they said.
An independent panel of experts found the early results of the study so compelling that they ordered the placebo portion of the study stopped early so that those participants could have access to the study medications.
The study was funded by the Bill & Melinda Gates Foundation.
The second study, called the TDF2 trial, directed by the CDC, tracked about 1,200 young, sexually active men and women in Botswana and Uganda. None had been previously infected with HIV.
They were randomly assigned to take either a daily placebo pill or Truvada.
After roughly three years, there were nine new HIV infections among adults taking Truvada compared to 24 in those assigned to the placebo, representing a 63% reduction in infection risk.
Among those who were thought to have taken the study drugs as directed, protection was even greater, rising to 78%.
Researchers said adherence to the medication regimens was high. About 84% of people in the study took their pills as directed, as determined by pill counts at regular check-in visits.
Additionally, there were no safety concerns identified in either study.
Both studies are due to be presented next week at the International AIDS Society Meeting in Rome.
Applying the Study Findings to the U.S.
Independent experts said that while the study results appear to be very promising, it was unclear how they might translate to people in the U.S.
Bruce Hirsch, MD, attending physician of infectious disease at North Shore LIJ Health System in New York said most of his HIV-positive patients in committed relationships were already taking substantial precautions to avoid passing the virus on to their partners.
Those precautions include using condoms and taking antiretroviral medications, like the ones used in these studies.
When those drugs are taken by HIV-infected people, they can reduce the risk of transmission to uninfected partners by 97%, Hirsch says.
"I think of a person who would use this medication as a person who is not in a committed relationship, who is maybe an unusual combination of being responsible and not so responsible, who wants to make unsafe sex a little safer," Hirsch says.
"It's a little bit hard for me to conceive of a person so thoughtful and so health conscious that he or she would take this step but not use barrier precautions," Hirsch says.
It's also unclear whether insurance would pick up the tab when the drugs are used in healthy people. By some estimates, Truvada costs between $12,000 and $14,000 a year in the U.S.
"There are two key issues here: Who will have access to the drugs, and how do you decide distribution?" says Sandra I. McCoy, MPH, PhD, an epidemiologist at the University of California, Berkeley. "We have many resource-poor settings where treatment is not available to everyone who needs it already. That will be the next focus area of research, these implementation kind of questions."
According to a 2008 report from the CDC, 86% of new HIV cases in the U.S. were attributed to sexual transmission, 54% among men who had sex with men and 32% among heterosexual partners.
"It's nice to know that there are other means of preventing HIV," Hirsch says. "HIV is treatable, but still, getting HIV is a personal tragedy and any means to prevent this infection is important for us to know about."