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HIV Prevention Trials Show Flexibility in Antiretroviral Dosing

Truvada pills, initially used to treat people with HIV, are a main component of PrEP (pre-exposure prophylaxis), where the drug is used to prevent infection. (AP Photo/Jeff Chiu)

Conquering HIV, the virus that causes AIDS, has proved to be one of the greatest challenges of modern medicine. But researchers have found drugs that can significantly curtail HIV’s spread.

Studies emerging at this year’s annual meeting of the Conference on Retroviruses and Opportunistic Infections, held in Seattle, reveal that there’s no single dosing strategy that works for everyone who wants to protect themselves against the AIDS virus.

The antiretroviral drug Truvada has long been used to suppress HIV in infected individuals. It can also be taken by uninfected people to shield themselves from acquiring the AIDS virus from their HIV-positive partners. Using Truvada daily or before and after sex is called pre-exposure prophylaxis or PReP.

The good news from three, high-profile studies of PReP is that dosing can be flexible.

Truvada, a drug compound that combines emtricitabine and tenofovir, works well at preventing HIV.

The antiretroviral drug is the most effective at reducing the risk of infection when taken daily. But used before and after sex, as directed, PReP also significantly lessened the risk of HIV transmission.

Bob Grant, with the Gladstone Institute at the University of California San Francisco, helped lead the so-called HPTN067 trial, which involved 179 South African women.

Grant said those on a daily dosing schedule had the highest levels of Truvada in their bloodstream and seemed generally to prefer the regular routine.

“Because it allowed them to build habits around taking a pill a day," he said. "They didn’t have to think whether they were going to have sex the following day or not. They didn’t remember to have to take a pill after having sex. It was easier in some ways to just take a pill a day than to try to take pills before and after sex.”

In that trial, adherence was high. Ninety-three percent of women who took Truvada every day had therapeutic levels in their blood after ten weeks. At 30 weeks, the percent dropped to 79 percent because some women stopped taking the drug.

The latest results of the IPERGAY and PROUD trials were also unveiled at the conference. They involved men who have sex with men. Those who took PReP around the time of sexual intercourse saw a significant, 86 percent reduction in risk of infection with HIV.

In those trials, carried out in Britain, France and Canada, participants took four pills around the time of sex — two before an anticipated sexual encounter, another pill 24 hours after sex and a fourth pill, 24 hours after that.

While protection with both the daily regimen and use only around sexual encounters was statistically similar, Grant said people who use the antiretroviral drug intermittently are more likely to become infected.

“People [who] try to take pills every day, and if they miss an occasional dose, they are still protected," he said. "And if they take two pills before sex and two pills after sex, that may also be effective, but there’s no forgiveness for missed dosing.”

Experts say lifestyle is an important factor. While some people don't mind taking a pill everyday, some prefer not to or they worry about social stigma surrounding taking HIV medication when they are not infected.

But if adherent, the studies suggest that both daily and intermittent PReP are largely effective in stopping transmission of the AIDS virus.