TORONTO - Taking a daily dose of an antiretroviral drug long used to treat HIV has been found to significantly cut the odds of gay and bisexual men who engage in risky sex from becoming infected with the virus.
A study of almost 2,500 men published online Tuesday by the New England Journal of Medicine found that taking the once-a-day pill reduced the risk of infection in men by about 44 per cent compared to those given a placebo.
And those in the study who adhered most closely to the daily drug regimen -- dubbed pre-exposure prophylaxis, or PrEP -- had even higher prevention rates. Their risk of infection was up to 73 per cent lower than those taking a dummy pill, said lead researcher Dr. Robert Grant of the Gladstone Institute of Virology and Immunology in San Francisco.
The study is the first to provide evidence that the prevention method reduces HIV infection risk, at least in men who have sex with men, said Grant.
"The ... study proves that PrEP provides important additional protection against HIV when offered with other prevention methods such as HIV testing, counselling, condom use and management of sexually transmitted infections," he said. "As with other prevention methods, the greatest protection comes with consistent use."
Grant said the medication, which combines the antiretroviral drugs emtricitabine and tenofovir, could become an important tool in trying to halt the global spread of HIV, especially in hard-hit countries in sub-Saharan Africa, India and Asia.
But Dr. Philip Berger, a long-time Canadian AIDS specialist, said it's hard to imagine countries that have difficulty paying for medications to treat people already infected with HIV-AIDS could afford drugs aimed at preventing the disease.
And Berger, a physician at St. Michael's Hospital in Toronto, questions whether gay and bisexual men who engage in risky sexual behaviour with multiple partners would continue to take a daily preventive pill for what conceivably could be decades.
Dr. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, called the study result "an important finding that provides the basis for further investigating, developing and employing this prevention strategy, which has the potential to make a significant impact in the fight against HIV-AIDS."
"No single HIV prevention strategy is going to be effective for everyone, and it is important to note that the new findings pertain only to the effectiveness of PrEP among men who have sex with men and cannot at this point be extrapolated to other populations," Fauci said in a statement.
"Therefore, we must continue to conduct PrEP research among other study populations, such as women and heterosexual men, to provide a comprehensive picture of its potential utility as an HIV prevention tool."
A total of 2,499 men at high risk of HIV infection participated in the study, which was conducted at 11 sites in Brazil, Ecuador, Peru, South Africa, Thailand and the United States. Half of study participants received the PrEP pill, while the other half were given the placebo.
In all, 64 HIV infections were recorded among the 1,248 study participants chosen at random to receive the dummy pill, while 36 HIV infections were recorded among the 1,251 participants who got the drug.
