F.D.A. Panel Weighs Preventive Use of H.I.V. Drug

An advisory panel to the Food and Drug Administration is expected to vote Thursday on whether a drug already used to treat H.I.V. infection should also be approved to prevent it. Such a recommendation, if made, would mark the first time that government advisers have advocated giving antiviral medicine to healthy people who might be exposed through sexual activity to the virus that causes AIDS.

Studies have shown that people who take the medicine, Truvada, every day have a greatly reduced risk of infection.

The F.D.A. usually accepts the advice of its advisory panels, which are made up of outside experts, mostly from medical schools.

On Thursday morning, the panel evaluated studies of the once-a-day pill and heard scientific presentations about whether Truvada should be prescribed for people at high risk of infection, like gay men who have multiple sex partners, especially those who do not always use condoms, and people in relationships with someone who is H.I.V.-positive. Young black men who have sex with other men are at highest risk.

The drug is meant not to replace condoms and other safe-sex measures, but to be used with them for added protection.

Experts say better methods of prevention are needed because there are 50,000 new H.I.V. infections a year in the United States. Several speakers emphasized on Thursday that that number had not budged in 15 to 20 years. Counseling and condoms are not doing the job, they said, and many of the newly infected are men whose sexual partners do not realize they are H.I.V.-positive.

Worldwide, there were 2.4 million to 2.9 million new cases in 2010.

After the scientific presentations on Thursday morning, many panelists voiced concern about the possibility that people who become infected while taking Truvada could develop dangerous drug-resistant strains of the virus. And they asked why resistance occurs in people taking the medicine, given that it is such a powerful drug.

Dr. John W. Mellors, chief of infectious diseases at the University of Pittsburgh, said that one likely reason is that if people take the pills inconsistently, they may wind up with levels of the drug that are too low to prevent infection, but just high enough to allow resistance to occur.

An F.D.A. analysis found that people who are older and more educated are more likely to take the drug faithfully. So are men who reported having receptive anal sex without condoms. There is no data to tell whether Truvada would prevent H.I.V. infection spread by needle sharing.

Nausea and abdominal pain are common side effects for the first few weeks people take Truvada; those symptoms then diminish.

Because Truvada has already been approved to treat H.I.V. infection, doctors have been free to prescribe it for prevention, and some have been doing so. Prescribing a drug for something other than its approved purpose, called off-label use, is allowed by the F.D.A, though drug companies are not permitted to market or promote drugs for such uses.