A daily dose of an antiretroviral drug used to treat AIDS patients reduced the risk of HIV transmission by nearly 44 percent in a large international study of uninfected homosexual men and transgender men who have sex with men. Scientists say that although the results are very encouraging, more studies are needed to confirm the findings among other high risk populations.
The Chemoprophylaxis for HIV Prevention in Men, or iPrEX study, recruited 2,500 HIV negative or uninfected men in Brazil, Ecuador, Peru, South Africa, Thailand and the United States in 2007 to receive the antiretroviral drug Truvada or a placebo.
Truvada is a compound made up of two widely available generic AIDS drugs - tenofavir and emtricitabine.
At the end of the 14 month study, 100 men had acquired HIV. But there were 43.8 percent fewer infections among men in the treatment group than in the group that received the sugar pill.
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More striking, researchers say, was a 73 percent lower risk of infection among men who adhered most closely to the daily drug regimen.
"The bottom line is that this is a very significant finding in the quest toward developing more comprehensive ways of preventing HIV infection," said Anthony Fauci, director of the Institute of Allergy and Infectious Diseases at the U.S. National Institutes of Health, which sponsored the study led by researchers at the University of California, San Francisco.
Dr. Fauci says more studies will be conducted to learn whether the drug works just as well to prevent HIV transmission among other high-risk individuals, including heterosexuals, in countries where infection with the AIDS virus has reached near-epidemic proportions.
"Men who have sex with men, as we know, are at the higher level of risk among people who acquire HIV infection. And so if it works in these individuals, it is very likely we will see similar results in women as well as heterosexual men," he said.
"The results are very encouraging. And this study really represents a major advance in HIV prevention research," said Kevin Fenton, Director of the National Center for HIV/AIDS, Viral Hepatitis, STD and TB Prevention at the U.S. Centers for Disease Control and Prevention in Atlanta, Georgia.
But Dr. Fenton cautions that daily doses of Truvada, which cost between $5,000 and $7,000 per year in the United States, are unlikely to be widely available in the developing world -- at least, not right away.
He says he expects researchers will begin exploring the effectiveness of using less expensive antiretroviral drugs to protect high risk individuals.
Dr. Fenton says that any drug therapy, known as preexposure chemoprophylaxis, or PrEP, will need to be combined with other well-established prevention strategies to lower the risk of HIV transmission. "The reality is that PrEP is not going to be right for everyone. It's not 100 percent effective. And when it is used, it will have to be used in partnership with very comprehensive monitoring, support and prevention services," he said.
Dr. Fenton says such services include regular testing for other sexually-transmitted diseases that put individuals at higher risk for HIV infection, and education about risky lifestyle behaviors, such as drug abuse and unsafe sexual practices.
An article detailing the findings of the Chemoprophylaxis for HIV Prevention in Men study is published in The New England Journal of Medicine.