The HIV drug tenofovir is safe to be given to men at high risk of contracting the virus as a preventative measure, scientists said on Friday, but further trials are needed to test its efficacy.

Researchers from the Centers for Disease Control and Prevention (CDC) in the United States studied the safety of the Gilead drug in gay and bisexual men who did not have the human immunodeficiency virus (HIV) that causes AIDS and said their results showed there were no concerns.

“We didn’t find any increased risk of harm in medical terms, and on the behavioral side the preliminary work we’ve done also suggests there is no increased risk,” said Lisa Grohskopf, who led the study and presented the findings at the International AIDS Conference in Vienna.

The approach of taking a daily antiretroviral drug to try to prevent HIV infection is known as pre-exposure prophylaxis, or PrEP. Scientists around the world are currently conducting studies to see if it may be an effective way to reduce HIV infection in high-risk groups, including gay men.

A previous study in Ghana, Nigeria and Cameroon found that the drug was also safe when given to heterosexual women at high risk of contracting HIV.

South African researchers presented research at the Vienna conference on Monday which showed that a microbicide gel also containing Gilead’s tenofovir can sharply reduce HIV infections in women.

More than 2.7 million people around the world become newly infected with HIV each year and 33.4 million people are currently living with the virus.

Although prevention methods such as using male or female condoms can be very effective, many people don’t use them and scientists are constantly searching for other ways of trying the prevent the incurable virus from spreading.

This trial looked at whether a 300 milligram tablet of tenofovir taken daily was safe among 400 HIV-negative gay men in San Francisco, Atlanta, and Boston.

The men were divided into four groups. Two groups were started immediately on either tenofovir or a placebo, or dummy pill, while the other two received either tenofovir or a placebo nine months after the start of the study. This design allowed researchers to compare risk behaviors among those taking a daily pill and those not taking pills.

“It is conceivable that if someone was taking a pill and thought that it was effective (in preventing HIV infection) that it might lead to a greater likelihood of risky behavior,” Grohskopf explained.

The researchers said they were “encouraged” that no serious safety concerns emerged in the trial. There were also no serious side effects and no significant differences in effect on kidney function between those taking tenofovir and those on a placebo.

“If PrEP proves effective it could provide an additional safety net for men who have sex with men and other individuals at high risk, when used in combination with other proven prevention strategies,” they said.

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By Kate Kelland

VIENNA (Reuters)