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By CNN.com

Researchers have shown for the first time, that a  combination of two antiretroviral drugs taken daily reduces the risk of HIV transmission in men and transgendered women having sex with men.  In the study, published in the New England Journal of Medicine, nearly 2,500 men were given either an oral combination of two widely used HIV medications  (emtricitabine and tenofovir) or a placebo. 

The risk of infection was reduced by almost 44 percent in the group getting the drugs. The risk was reduced even further– almost 73 percent –in study participants who took the drugs for most of the year.

“We now have strong evidence that pre-exposure prophylaxis with an antiretroviral drug, a strategy widely referred to as PrEP, can reduce the risk of HIV acquisition among men who have sex with men, a segment of the population disproportionately affected by HIV/AIDS,” says Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID), part of the Institutes of Health.

 “Additional research is needed, but certainly this is 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,” Fauci tells CNN.

Researchers found people who took the PrEP pill regularly–at least 90 percent of the year –actually reduced their risk of infection by more than 70 percent.  Side effects were minor.  According to researchers, a small number of participants of the phase III trial experienced nausea. Slightly elevated creatinine levels were found,  but they were resolved spontaneously or once the drug was stopped.  Creatinine is a muscle waste product. It’s measured in blood and urine and is an indication of your kidney function.

Researchers found no evidence of drug resistance.

Study participants were followed for up to three years.  All received HIV testing, condoms, and safe sex counseling and treatment for any sexually transmitted diseases.

Dr. Michael Saag, director, Center for AIDS Research at the University of Alabama at Birmingham, and Immediate Past President of the HIV Medical Association is concerned about exposing uninfected people to drugs that he says are known to have potentially harmful side effects, no matter how uncommon, and whether it’s cost effective. “With the limited resources around the U.S., I would much rather see us spend our money finding the 25% of people in the country who are HIV infected but don’t know their status.” 

Saag believes getting them tested and treated is more important. “Outside of the benefit to them for their own health there would be a definite prevention benefit to society because that 25 percent of people who don’t know their status are responsible or over 60% of the new infections per year – roughly 30,000 new cases per year –  and to me it would be much more beneficial to put our efforts in that area before we start figuring out ways to pay for medicine to protect a relatively few number of new cases through PrEP,” Saag says.

Fauci said while it’s too early to recommend who should take PrEP, the study results are a proof of concept and should be looked at as another tool in the prevention basket.  Still, it’s important, he says, to understand that this study looked at only one population, so additional information is needed.

Researchers say the study was conducted in men who have sex with men because they are disproportionately affected by HIV/AIDS. In the U.S. alone, 53 percent of all new infections are in this population.