WEDNESDAY, May 9 (HealthDay News) -- U.S. Food and Drug Administration advisers will meet Thursday to decide whether to endorse the use of the drug Truvada as a means to help prevent HIV infection in people at high risk.

Those individuals might include highly sexually active gay or bisexual men, or the partners of people already infected with HIV, the virus that causes AIDS.

A report released by the FDA this week ahead of Thursday's meeting suggests that experts do believe the drug is safe and effective for this use.

There are potential drawbacks to using the medication in this way, however. Truvada -- which combines two HIV-fighting drugs, tenofovir (Viread) and emtricitabine (Emtriva) -- is very expensive and may cause side effects. And although doctors can already prescribe it to people trying to avoid HIV infection, critics say it's too early to officially allow it to be promoted for that use.

On the other hand, those who support marketing the drug as a preventive agent say it can help high-risk people avoid the disease, especially if they don't use condoms or if they want an added layer of protection.

"I don't see it as a panacea, but it's an option, and that's important," said Dr. Kenneth Mayer, an AIDS specialist and medical research director of The Fenway Institute at Fenway Health in Boston. "Some people won't use a condom, but will say, 'if you give me another option, I'll use that.'"

Truvada works to prevent HIV from replicating in the body's cells. Mayer explained that in someone who is not yet infected but is exposed to HIV, the drug may prevent the virus from reproducing even if it's already invaded cells. As a result, he said, "the virus cannot start turning the newly exposed person's body into a 'factory' to produce more HIV particles."

A study published in 2010 in the New England Journal of Medicine found that Truvada cut the risk of HIV infection by almost 44 percent in those at highest risk for contracting the virus, namely sexually active gay and bisexual men. The risk reduction climbed to nearly 73 percent among study participants who took the pill 90 percent of the time, the researchers added.

On Thursday, the FDA advisory panel will meet and come up with advice for federal officials about the possible marketing of the drug as a preventive agent by its manufacturer, Gilead Sciences.

The research suggests that people who use Truvada daily along with condoms would gain an added layer of protection, because condoms aren't 100 percent effective. But one organization, the AIDS Healthcare Foundation, worries that wider use of the drug could lead to more infections by discouraging people from bothering to use condoms.

"Why would you take this medication if you intended to use condoms?" asked the group's president, Michael Weinstein, in an interview with Bloomberg News. He used a sartorial metaphor to elaborate how unlikely that might be: "You've got to be really paranoid about your pants falling down to wear a belt and suspenders."

A. David Paltiel, a professor at Yale School of Medicine, said his research has shown that the use of preventive drug treatments should reduce the risk of infection overall. Still, he said, it's unknown if "people (would) take more chances because they feel protected by a 'chemical condom.'"

Potential markets for Truvada as a preventive drug, Mayer said, include gay men who have sex with more than one man and any committed couple in which one person is HIV-positive, including some heterosexual couples who want to have children.

Mayer, who has conducted research into the drug, said that allowing the marketing will probably lead to an increase in its usage for prevention. But, "this is not a one-time, end-of-the-problem approach like a shot of penicillin to treat an infection like syphilis," he said. "Also, it involves someone perceiving that he or she is at risk, or a provider being comfortable enough to ask about a person's risk. We know that a lot of health providers don't like to talk to their patients about sex."

Truvada can also cause a long list of side effects, including gastrointestinal problems. And it's costly, with prices in the United States tagged at about $26 a day or $10,000 a year. Still, a study released this year found the drug would be cost-effective if used extensively by gay and bisexual men at high risk of becoming infected.

For his part, Paltiel said his research came to the same conclusion: That widespread usage of the drug in high-risk people would be "as cost-effective as other widely accepted public health and medical interventions."

More information

Find out more about HIV/AIDS at the U.S. National Library of Medicine.