Could AIDS drugs stop us from getting HIV?

Frustrated by recent failures of AIDS vaccine trials, some advocates are pinning their hopes on pills that would prevent HIV infection.
By next year, the New York Times reports today, more people will be enrolled in preventive-drug studies than in trials of HIV vaccines and microbicides — gels or foams that would be used during sex to destroy the virus or prevent it from causing infection.
As many as 15,000 people are expected to take part in the pre-exposure prophylaxis trials, also known as PrEP, by mid-2009, according to a report by the AIDS Vaccine Advocacy Coalition that was presented yesterday at the 17th International AIDS Conference in Mexico City. The trials are testing two existing AIDS drugs, tenofovir by itself or in combination with emtricitabine, according to the Times.
Microsoft founder Bill Gates, whose foundation is spending $93 million on PrEP studies, told the Wall Street Journal that the drug regimens are the most realistic, up-and-coming prevention tools.
“If you ask me what will come first,” Gates told the Journal, “something like PrEP has a good chance of becoming available before we have a 100%-efficacious vaccine. The challenges are a little less daunting. If we have that tool, it could have a very big impact.”
While early PrEP trials have shown promise in staving off a virus similar to HIV in primates, and the drugs are safe in humans, it remains to be seen how the medicines would work best as a form of prevention, the Times notes. Would they need to be taken every day, or only before sex? And would they be used in combination with existing preventive methods, such as condoms?
Scientists have been trying to develop a vaccine against HIV since nearly the start of the quarter-century old epidemic. More recently they turned to microbicides, but those, too, have proven disappointing.

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