A new study shows that anti-retroviral drugs can be used to prevent HIV infection in uninfected people.  It?s called PrEP ? or pre-exposure prophylaxis.

The findings, released Tuesday, appear in the New England Journal of Medicine.  Researchers say it could ?fundamentally change strategies to slow the global HIV epidemic.?

The iPrEx study was sponsored by the U.S. National Institutes of Health through a grant from the non-profit Gladstone Institutes, which are affiliated with the University of California at San Francisco.

Take a pill

Mitchell Warren, head of the AIDS Vaccine Advocacy Coalition in New York, has been following the iPrEx study.  He says, ?The idea of pre-exposure prophylaxis is basically to take a pill in advance of exposure.  And this is not unique to HIV.  Travelers do this all the time with malaria prophylaxis.?

PrEP has been receiving more attention over the last five years among AIDS researchers.

?The anti-retroviral pill ? the same one that treats many people with HIV ? might actually have a preventive effect,? he says.

The iPrEx study is the first of several studies on the efficacy of PrEP.

Warren says, ?This is the first one at all representing results.  And the results are very, very positive and very exciting.  They are very specific.  This trial took place among men and transgender women, who have sex with men in six countries around the world.?

The study was conducted at 11 sites in South Africa, Brazil, Ecuador, Peru, Thailand and the United States.  The drugs used in the study were a combination of tenofovir and emtricitabine.

Fundamentally change HIV strategies

?We know we have incredibly powerful prevention options already, most importantly the male and female condoms.  Those don?t change.  We need those products,? he says.

But warren adds, ?We now have a back-up, an additional tool.  And it?s important to recognize that in the trial it?s not just saying the pill worked.  The pill provided 44-percent additional protection on top of the standard, state of the art prevention services that were being provided in the trial.?

He says this is important news for those who have little choice in saying whether a condom will be used during sex.

Simple, but?

Taking a pill appears simple enough, but apparently not simple enough for everyone.

?The good news is for those participants who did take their pill on a regular, consistent basis, they seemed to have higher levels of protection.  The challenging news though is that there weren?t that many people who were able to adhere to that regimen,? he says.

He says more research should be done on the effectiveness of PrEP if the pill is not taken on a regular basis.

?Is it more feasible and more acceptable to people, but does it still provide protection.  And that doesn?t get answered in this study,? he says.

The drugs are powerful and can have side effects.  That?s something that should be kept in mind before attempting to use them as a prevention method.  However, another problem was also uncovered in the study.

?There were two cases of resistant HIV that seemed to have been caused by people taking PrEP when they were already infected, but didn?t know it. So it really highlights that for Prep to be effective you?ve got to have confirmed HIV negative status before you start taking PrEP,? he says.

Nearly 2500 individuals took part in the study.  Tenofovir, one of the drugs used in the study, was also an ingredient in the promising microbicide CAPRISA 004, which received much attention earlier this year.