The Food and Drug Administration approved Monday the first pill aimed at preventing HIV infections in healthy people who risk contracting the disease through unsafe sex.

The medication, Truvada, is the first drug shown to protect people from becoming ­infected with HIV, the virus that causes AIDS. It is already used to treat HIV-positive ­patients.

“New prevention methods are needed in order to have a major impact on the HIV epidemic in this country,” Dr. Debra Birnkrant, director of the division of antiviral products at the FDA, said during a press conference.

She said the overall rate of new infections has remained stable, but “we continue to see about 50,000 adults and adolescents diagnosed with new HIV infections each year. ­Infection rates among men who have sex with men, particularly among young minority men, have increased significantly.”

Truvada is intended for adults at high risk of contracting HIV, which include sexually active gay men and healthy partners of HIV-infected individuals, whether heterosexual or homosexual.

The manufacturer, Gilead Sciences, did not have an estimate of the number of people who might take the drug to prevent HIV infections.

“I think the uptake is going to be slow but steady,” predicted Dr. Kenneth Mayer of the Fenway Institute, a Boston HIV research center that particpated in one of the clinical trials of Truvada.

Truvada is expected to cost at least $13,900 a year for treatment in the United States, according to California-based Gilead, but consumers would pay much less if their insurers cover it. Harvard Pilgrim Health Care said Monday it will cover Truvada as a preventive medication, as it already does for HIV treatment, at a cost of about $25 to $30 per month for patients. Representatives of Blue Cross Blue Shield of Massa­chusetts, the state’s largest health insurer, and Tufts Health Plan said the companies will review whether to cover the drug for HIV prevention.

The FDA decision is supported by several clinical studies, including the one conducted at the Fenway Institute and other sites around the world. The study followed 2,499 HIV-negative men and transgender women who had sex with men, including some who were infected with HIV. After an average of two years, those who were assigned to take Truvada daily — although many failed to follow the daily regimen — had a 44 percent lower risk of acquiring HIV than participants given a placebo.

“Getting people to take pills on a daily basis — people who are healthy — is the challenge,” said Mayer, who was the principal investigator of the Fenway research project.

Birnkrant echoed that concern, saying adherence to the daily regimen was low, around 30 percent.

If participants stuck with the regimen and had high levels of the drug in their blood, Mayer said, they were less likely to get HIV, with protection rates approaching 90 percent.

Another trial involving heterosexual couples where one partner was infected and condoms were used routinely found Truvada reduced the risk of infections by 75 percent.

Truvada (a combination of two drugs with the generic names emtricitabine and tenofovir disoproxil fumarate) is ­already used with other anti­retroviral drugs to treat HIV. For prevention purposes, the FDA now recommends the drug as part of a comprehensive HIV prevention strategy including safe sex practices — using condoms and avoiding sex with multiple partners at high risk of infection — risk ­reduction counseling, and regular HIV testing.

Public health specialists worry that if the drug is not used correctly, people could develop drug-resistant HIV strains that will stop responding to Truvada. That could happen if individuals do not take the drug daily and become ­infected. The drug can lose its potency in such newly infected people, or in people who are unaware that they are infected, if taken alone, without the other antiretroviral drugs it is combined with to treat infected ­patients.

For that reason, only people who have tested negative for HIV can get the drug for disease prevention.

As a condition of approval, the FDA is requiring Gilead to investigate possible drug resistance in those who acquire HIV while taking Truvada. The company also will be required to collect data on women who become pregnant while taking the drug because safety risks to the fetus remain unknown.

News Source: Boston Globe

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