Experts in HIV-AIDS are hailing the discovery that an antiretroviral medication appears to also prevent HIV infection as an important finding, but say the medication can't replace condoms.

The study, released Tuesday in the New England Journal of Medicine, looked at Truvada, a medication already used in HIV patients to reduce their "viral load" -- the amount of the virus in their bodies. The research found that when uninfected gay and bisexual men took the medication daily, it helped reduce their risk of acquiring HIV.

The pill reduced the risk of infection by about 44 per cent compared to those given a placebo. Those participants who adhered most closely to the daily regimen had even higher prevention rates.; their risk of infection was up to 73 per cent lower than those taking the dummy pill.

Dr. Robert Hogg of the B.C. Centre for Excellence in HIV/AIDS, says while the finding is exciting, the study looked at a very specific population group.

"This is a dramatic finding, and in terms of the prevention, it is a very interesting one," Hogg told CTV's Canada AM Wednesday. "But we have to put it into context. In terms of other prevention activities, it's not going to replace condoms."

Hogg says he thinks the medication might be useful for people who are at high risk of contracting HIV, but might not be suitable in other people.

He noted that the researchers noticed that some participants taking the drug developed kidney problems that resolved when they stopped the medication.

"It will be important for sex workers who are having trouble using condoms. This will be a great prevention method to reduce the risk, but it's not going to replace other prevention methods, like condoms or peer-to-peer education or other means of HIV prevention," Hogg said.

The study looked at 2,499 men at high risk of HIV infection in 11 sites in Brazil, Ecuador, Peru, South Africa, Thailand and the United States.

Half the participants received the pill, which combines the antiretroviral drugs emtricitabine and tenofovir, while the other half were given the placebo. Both groups were told to continue using condoms since neither group knew if they were taking the real medication.

In all, 64 HIV infections were recorded among the 1,248 study participants chosen at random to receive the placebo, while 36 HIV infections were recorded among the 1,251 participants who got the drug.

Lead researcher Dr. Robert Grant of the Gladstone Institute of Virology and Immunology in San Francisco said pre-exposure prophylaxis, or PrEP, 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 many have questioned whether that's likely, given that many developing countries already have difficulty paying for medications to treat HIV-AIDS.

Even in the U.S., there are questions about who would pay for the meidcation, which could US$5,000 to $14,000 a year.

Kyriell Noon of the San Francisco-based Stop AIDS Project told the Associated Press that a lack of access to education and health care already contribute to HIV infection rates, so he wonders whether those who would benefit from the drug would be able to access it.

"The history of the HIV epidemic in this country has been a story of disparities," he said. "I would hate to see this new exciting breakthrough enhance those disparities."

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."

With a report from the Associated Press