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SEATTLE -- Pre-exposure prophylaxis (PrEP) with a single pill prevented HIV infection among more than 85% of two groups of men who have sex with men, according to two studies presented here.

The studies attempted to approximate a real-world use of oral PrEP and both had surprisingly high efficacy rates -- 86% in both cases, researchers reported at the

That level of efficacy was sufficiently high that both studies were stopped early by their monitoring committees.

The research, taken together, has "absolutely solidified our understanding" of how valuable PrEP can be in men who have sex with men, commented of the University of Pittsburgh School of Medicine.

Sometimes controversial, the use of PrEP has been growing since early studies showed that -- among men at high risk of HIV -- taking an anti-HIV pill a day could cut the risk of infection by about 44%.

Hillier, who moderated a session at which the new research was presented, told 口袋女优 the studies "cement" the conclusion that PrEP can work for men who have sex with men.

PrEP "should be offered more widely," she said.

The two studies took different approaches.

In the so-called PROUD trial, investigators led by , of the United Kingdom Medical Research Council, attempted to approximate a real-world setting.

Among high-risk but HIV-negative men attending some 220 sexual health clinics, they randomly assigned some to begin 2 years of PrEP with a daily pill of tenofovir/emtricitabine (Truvada) while others were assigned to delay taking the pill for a year before also starting PrEP.

In effect, the participants who deferred amounted to a placebo group, although the study had an open-label design, McCormack said. The goal was to see if efficacy would be as good as the 44% seen in the earlier iPrEx trial.

The study was initially thought of as a pilot study to see if the researchers would recruit and retain enough participants. But the results were so striking that the data monitoring committee said last October the researchers should offer PrEP to all participants, McCormack said.

In the IPERGAY trial, researchers led by , of the University of Paris Diderot in Paris, enrolled high-risk men in a blinded placebo-controlled trial of "on-demand' PrEP.

Participants were told to take two pills between 2 and 24 hours before having sex, another 24 hours afterwards, and a fourth 24 hours after that. Volunteers were randomly assigned to get tenofovir/emtricitabine or a matching placebo.

The goal was to see if the protection remained, even though participants were taking fewer pills than in earlier trials, but taking them at "the right time," Molina told 口袋女优.

Again, the benefits were so apparent that the data monitoring committee in October suggested the placebo arm be closed and all participants be offered the on-demand PrEP, he said.

In the U.K. trial, McCormack and colleagues recruited 545 men who reported having recent unprotected anal sex and randomly assigned them to start or to defer daily oral PrEP.

Overall, 22 participants acquired HIV, for an incidence rate of 4.9 per 100 person-years, she reported.

But among those on PrEP, the rate was just 1.3 cases per 100 person-years on the basis of three infections, compared with 8.9 per 100 person-years among the deferred participants, based on 19 infections.

The rate in the deferred group was about three times higher than anticipated, but even had it met expectations, the rate among the PrEP group would have amounted to a 50% reduction in risk, McCormack told 口袋女优.

As it was, the efficacy was 86% (P=0.0002) and the number needed to treat in order to prevent one infection was 13, she reported.

Interestingly, the two groups both began with irregular condom use, but there was no evidence that the PrEP participants increased risky sex. Indeed, McCormack reported, both groups had similar rates of sexually transmitted infections other than HIV, suggesting they had not changed their behavior.

As well, self-reported sexual behavior did not change, she said.

In the French trial, Molina and colleagues randomly assigned 414 high-risk men to get either PrEP or a matching placebo, with instructions to use the pills around the time of sex.

Again, the men were eligible if they reported recent unprotected anal sex but did not have HIV.

As in the PROUD trial, researchers expected to see about three infections per 100 person-years in the placebo arm, but instead they saw 6.6, based on 14 new cases of HIV.

In contrast, there were just two new cases in the PrEP arm, yielding a rate of 0.94 cases per 100 person-years.

The relative risk reduction was 86% (P=0.002) and the number needed to treat to prevent one infection was 18.

Interestingly, Molina noted, the two men who acquired HIV in the PrEP arm were shown to have stopped taking the drug some months before they became infected.

On average, participants took about 16 pills a month, and adherence was similar between the arms. But participants did not necessarily take their pills for each sexual encounter, he said.

The data from the two trials is "incredibly robust," commented

"It does nail it," he told 口袋女优. "Oral PrEP with Truvada is incredibly effective when used correctly and consistently."

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