Many experts say the drug will help hasten the end of the AIDS pandemic. But experts in Brazil say the drug alone isn't the answer.
One of the drug trials the FDA considered was done at the Oswaldo Cruz Foundation Research Institute, also known as Fiocruz, in Rio de Janeiro.
Researchers at the institute enrolled 200 gay men in the study. Half were given Truvada, a drug that's already used to treat people who have HIV.
The other half were given a placebo.
The men were recruited from gay night clubs and bath houses in Rio. By their own descriptions of their sex lives, they were categorized by the researchers as being at high risk of getting the virus.
Brenda Hoagland, the medical coordinator of the study at Fiocruz, says the trial showed that Truvada was safe to use and offered a high level of protection against HIV when taken every day. But she adds that Truvada is not a magic bullet.
"It's not for everybody," she says. "It's for those people who really have a risk," like sex workers or someone who's partner is HIV positive.
Dr. Valdiléa Veloso, the head researcher on the trial at Fiocruz, says to stop the spread of HIV public health officials have to be realistic and recognize that condoms alone haven't stopped the spread of the virus. And she says, doctors need more tools to try to rein in HIV.
"Some people just don't like to have sex with condom and people have the right to do it," Veloso says.
For the most part the AIDS epidemic in Brazil remains concentrated among prostitutes, intravenous drug users and gay men.
Veloso thinks it would make sense to make Truvada available along with safe sex counseling to some gay youth. "Not a widespread use," she says. "But a target use for people that can use it maybe for a while, maybe for some years and then stop when they're older and more mature."
There's concern among some groups that a drug that blocks the transmission of HIV could be a set-back for safe sex campaigns and might actually encourage unsafe sexual behavior.
Mauro Schechter, a professor of infectious diseases at the Federal University of Rio de Janeiro, was running one of the other trials of Truvada.
A decade ago Schechter faced similar criticism for research he did showing that giving someone anti-AIDS drugs after a high-risk sexual encounter can also reduce the chance of HIV infection. He says these critics as well as some anti-AIDS programs are out of touch with the real world where the virus gets transmitted.
"People will always have sex. There will always be people taking drugs, always people drinking," Schechter says. "These things will always happen. It's our role as scientists to develop as many preventative tools as we can. And then it's the role of public health officials to decide how to use them."
Truvada as an HIV prevention drug is more likely to be offered in the U.S. before it's available in Brazil. That's because it costs roughly $1000 a month. And it's not licensed in the South American nation. Health officials in Brazil say the country may be able to do something similar but with a generic HIV drugs already on the market.