AIDS Drugs Show Promise at Preventing Infection; Global Studies Expanded

A prophylactic drug combination to prevent HIV infection has proven so effective in animal studies that CDC announced last week it is expanding ongoing human safety and efficacy tests.

The two drugs, Viread (tenofovir) and FTC, or Emtriva (emtricitabine), or Gilead Science Inc.'s pill combining the two, Truvada, are already used to control infection in patients with HIV. The drugs are also used in post-exposure prophylaxis for health care workers and to prevent mother-to-child transmission. Some doctors have prescribed them as an off-label HIV-preventive for patients who admit not using condoms. As this type of use could breed drug resistance, scientists are rushing to expand the studies.

In monkey studies, Tenofovir has previously been found to be a partially effective HIV prophylactic. Unlike earlier AIDS drugs, it does not interact with other medicines or birth control pills, is long-acting in the blood, and is less apt to cause viral resistance. Scientists began studying the FTC-tenofovir combination after Truvada entered the market last year.

In a 14-week study of macaques rectally exposed each week to a simian-human HIV strain, no monkeys getting the drugs were infected. All but one of those not taking them got infected, usually after two exposures. The results were reported last month at the 13th Conference on Retroviruses and Opportunistic Infections in Denver.

"We wanted to see, was the drug holding the virus down so we didn't detect it," or was it truly effective, said Thomas Folks, head of CDC's HIV research lab. "We're now four months following the animals with no drug, no virus. They're uninfected and healthy."

Last year, CDC allocated $19 million to study tenofovir in Thailand injection drug users, high-risk heterosexuals in Botswana, and gay men in Atlanta and San Francisco. A third U.S. city, not yet identified, is being added, CDC said last week. The Botswana study is switching to the combination drug; the others were already advanced using tenofovir alone.

The most advanced prophylactic drug trial is a Family Health International study among 400 heterosexual women in Ghana, which receives funding from the Bill & Melinda Gates Foundation. The National Institutes of Health is beginning a tenofovir study among 1,400 gay men in Peru. Government and private agencies are considering others. Tenofovir is also being studied as a vaginal microbicide gel for women.

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