Innovation & Technology April 1, 2010, 5:00PM EST

Will an AIDS Pill a Day Keep the Virus Away?

Drugmaker Gilead is betting the one-pill PrEP treatment will slow the virus' spread—as are some of the world's top health agencies and philanthropists

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The 30-year war on AIDS has produced its share of notable victories. In the U.S., behavioral changes and combination drug therapies brought down the AIDS-related death toll from a peak of nearly 52,000 in 1994 to about 14,600 in 2007, according to the Centers for Disease Control & Prevention. Yet HIV infections are still spreading rapidly in parts of Africa and Asia. And so far, efforts to find a cure or develop a vaccine that would stop HIV in its tracks have failed.

What if there were another way to slow the pandemic? Gilead Sciences is helping to test a different prevention strategy, which involves dosing individuals at risk of contracting AIDS with drugs normally used to treat people who are already infected. This approach, known as PrEP (pre-exposure prophylaxis), is being tested in 10 clinical trials involving more than 20,000 people in the U.S., Africa, Asia, and Latin America. Gilead has supplied many of the drugs for the trials. Other backers include the CDC, the National Institutes of Health, and the Bill & Melinda Gates Foundation. Researchers expect initial results in July.

If the data are positive, the approach could have a big impact on the AIDS pandemic—and on Gilead, says Leerink Swann analyst Josh Schimmer. He says PrEP could bring the Foster City (Calif.) company as much as $1 billion in sales in the U.S., where the number of infections among gay men has been rising since 1991, according to the CDC. Gilead pulled in $5.54 billion last year in sales of its top three AIDS drugs—Truvada, Atripla, and Viread—which are taken by 85% of U.S. patients as a first defense against the virus.

In the PrEP trials, Viread or Truvada is administered to uninfected people from groups most at risk of contracting the virus. The studies are also designed to determine whether those receiving the drugs take greater risks in the belief they're protected against the virus. Participants receive counseling on ways to avoid infection.

Speaking to a U.S. Senate committee about global health priorities on Mar. 10, Bill Gates said that, if the trials produce positive results, PrEP distribution programs could begin in developing countries in 2012. "PrEP is the next big thing," says Mitchell Warren, executive director of the New York-based AIDS Vaccine Advocacy Coalition. "We have a level of biological plausibility and early data in animal studies that is stronger than anything we have seen in the other approaches." A study presented last year at the Conference on Retroviruses and Opportunistic Infections (CROI) meeting in Montreal found Truvada cut the risk of infection almost sixteenfold in monkeys.

There are also precedents for such intervention. Drugs made by GlaxoSmithKline (GSK) and Boehringer Ingelheim are already used to prevent the virus from passing to babies in the wombs of infected mothers, and Glaxo's Combivir is prescribed to prevent infections in men who take it after unprotected sex with an HIV-positive partner. "I'm very hopeful that this approach will help to reduce HIV infection rates," says Dawn K. Smith, a researcher at the CDC who's devising plans to implement the strategy if it proves effective. "But I want to see the trial results before I call myself a believer."

TOO COSTLY?

The world needs new tools to fight AIDS, which is responsible for more deaths than any other infectious disease. About 33 million people live with HIV, according to UNAIDS, the coalition of U.N. agencies formed to fight it. In 2008, 2.7 million people were newly infected with the virus, and 2 million died from AIDS-related complications.

There could be downsides to PrEP. Gilead acknowledges that healthy patients who take AIDS drugs over the long term could experience side effects. And if the promise of protection from HIV appears to spur those at risk to take fewer precautions, the entire PrEP effort could suffer a black eye.