Since 2010, when a landmark study in the New England Journal of Medicine found that giving a daily dose of Gilead Sciences' Truvada to men who have sex with men can reduce HIV infection rates by 44 percent, researchers have been trying to work out how to make this treatment approach financially feasible.

Gilead is seeking permission for Truvada -- a combination of its HIV drugs Emtriva, also known as emtricitabine, and Viread, or tenofovir -- to be used as a form of "pre-exposure prophylaxis," often shortened to PrEP.

The drug is already approved to treat people infected with the human immunodeficiency virus that causes AIDS.

A prior study found that giving Truvada to all men who have sex with men -- who account for more than half of the estimated 56,000 new infections annually in the United States -- was too costly.

The latest study from a team at Stanford University estimates that giving a daily preventive dose of the drug to all U.S. men who have sex with men would cost $495 billion over 20 years in terms of the cost of drugs and healthcare visits, the team reported in the Annals of Internal Medicine.

And giving the drug to healthy men to prevent a future infection might come at the expense of treating people who are already infected with HIV, the virus that causes AIDS, they said.

Instead, the team looked specifically at men who are high risk of developing HIV -- those who have five or more sexual partners a year.

If just 20 percent of these high-risk individuals took the drug it could prevent 41,000 new infections over a period of 20 years, at a cost of about $16.6 billion during that period, the team found.

By targeting this high-risk group, the team estimates the treatment could prevent twice as many infections as it could if given to 20 percent of the general population of men who have sex with men, and it would offer a better value.

"Use in high-risk men who have sex with men would provide substantial health benefits at a lower cost, although the budgetary effect would still be sizeable," Jessie Juusola, a PhD. candidate at Stanford, and colleagues wrote in the Annals of Internal Medicine.

The team said the findings can help shape doctors and policymakers' decisions about which patients should get the drug.

An estimated 1.2 million Americans have HIV, according to the Centers for Disease Control and Prevention.

In preliminary guidelines issued last year, the CDC said only high-risk gay and bisexual men should use a daily AIDS pill to protect themselves from the virus.

An FDA advisory panel is expected to consider in mid-May whether to allow use of the drug as a way to prevent HIV infection in healthy people.

(Reporting By Julie Steenhuysen; Editing by Andrew Hay)

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