Aug. 4 (Bloomberg) -- Drugs made by Gilead Sciences Inc. that have been shown to treat the AIDS virus will be tested in healthy people to see if they can prevent the lethal disease.

Seven large studies using daily doses of Gilead medicine to prevent HIV in people at high risk of infection have begun or are planned to start over the next four years, according to the AIDS Vaccine Advocacy Coalition, a New York-based group that promotes prevention.

The backfire of Merck & Co.'s AIDS vaccine, along with similar disappointing results from gels designed to protect women from HIV, have sent researchers in search of new preventive tools. Studies of drugs by Gilead, based in Foster City, California, might show whether the approach works years before research on new vaccines and microbicides is complete, said Mitchell Warren, the coalition's executive director.

``This looks like it's going to get us answers faster than anything else,'' Warren said in an interview yesterday at the 17th International AIDS Conference in Mexico City. ``We need to be ready to start implementing this approach if these trials give positive results.''

Gilead rose 15 cents to $53.84 at 4 p.m. New York time in Nasdaq Stock Market composite trading. The shares have gained 17 percent this year. Gilead's AIDS drugs sold $3.14 billion last year.

Stopping New Cases

New approaches to prevention are a top concern for AIDS researchers, advocates and patients at the conference. About 2.7 million people catch the virus each year, and 33 million are infected worldwide, according to UNAIDS, the United Nations agency that coordinates research and care.

The trials will examine the use of single daily doses of Gilead's Viread and Truvada, alone or in combination, for pre- exposure prophylaxis, or PrEP. As many as 16,000 healthy, uninfected people will be in PrEP studies by late 2009, more than are planned to be in all the world's late-stage vaccine and preventive gel trials combined at that time, Warren said.

Gilead sells a month's supply of Viread to U.S. wholesalers for about $552 per month. A month's supply of Truvada, a combination of Viread and another antiviral, costs about $840, said Amy Flood, a company spokeswoman, in an e-mail today. The company charges people in poor countries about $17 a month for Viread and $26 a month for Truvada, and a generic version of Viread is slightly cheaper, she said.

Possibility of Resistance

Early studies of tenofovir, the active ingredient in Viread, suggested that it might play a role in prevention, said Jim Rooney, Gilead's vice president of clinical research. An injected form of the drug prevented monkeys from getting an HIV-related virus, he said.

Gilead went on to develop the drug as a pill for treatment. Discussion of its preventive possibilities began almost as soon as it got market clearance, said Lynn Paxton, who's coordinating prevention trials of Gilead's drugs for the U.S. Centers for Disease Control and Prevention in Atlanta.

Doctors use drugs to prevent HIV in people exposed to the virus through accidental needle sticks. Drugs can also prevent babies from getting the virus from their infected mothers at birth or during breastfeeding.

PrEP might involve giving people antiviral drugs for years at a time, and that might breed drug-resistant strains in people who nonetheless become infected with HIV, said Charles Gilks, treatment coordinator for the World Health Organization's department of HIV/AIDS.

Reducing Risk

``We don't know which way it's going to go at the moment,'' he said July 31 in a telephone interview. ``You could argue that probably only a very few people will develop resistance, but for individuals who do, it would limit their treatment options.''

To be worth the risk of giving to healthy people, PrEP would have to prevent infections in at least 60 percent of people who take the drugs, said Robert Grant, an associate investigator at the Gladstone Institute of Virology and Immunology in San Francisco, who's running one study of Gilead's drugs in the U.S. If it works, PrEP would probably drive the number of drug- resistant cases down, he said.

``The best way to prevent HIV drug-resistance is to prevent HIV infections,'' he said at the conference.

Other antiviral drugs are associated with side effects such as anemia, pancreatitis, and liver damage, she said. Only a drug with an excellent safety record could be used for prevention in healthy people, CDC's Paxton said. HIV also has some difficulty mutating into forms that resist Viread, she said.

No `Financial Opportunity'

Family Health International, a public-health research group in Durham, North Carolina, along with the CDC, the National Institutes of Health, the Seattle-based Bill & Melinda Gates Foundation, and the Pittsburgh-based Microbicide Trials Network that studies HIV prevention gels, all are sponsoring studies of Viread and Truvada.

Demand for PrEP drugs will probably be restricted to high- risk patients in the U.S., and supplies for most poor nations could be produced by makers of licensed generic versions.

``We're not looking at this as a financial opportunity,'' said Gregg Alton, the company's senior vice president and general counsel, at the conference.

To contact the reporter on this story: John Lauerman in Boston at jlauerman@bloomberg.net.

Last Updated: August 4, 2008 16:28 EDT