Use of HIV medications reduces risk of HIV infection in uninfected people

In a finding with the potential to fundamentally change strategies to slow the global HIV epidemic, a new study called iPrEx shows that individuals at high risk for HIV infection who took a single daily tablet containing two widely used HIV medications, emtricitabine and tenofovir (FTC/TDF), experienced an average of 43.8% fewer HIV infections than those who received a placebo pill (95% CI 15.4 to 62.6%; P=0.005). The study, reported in the New England Journal of Medicine, is the first evidence that this new HIV prevention method, called pre-exposure prophylaxis or PrEP, reduces HIV infection risk in people.

A total of 2,499 individuals at high risk of HIV infection participated in the six-country iPrEx study. All study participants received a comprehensive package of prevention services designed to reduce their risk of HIV infection throughout the trial, including HIV testing, intensive safer sex counseling, condoms and treatment and care for sexually transmitted infections. Half of study participants also received the PrEP pill, while the other half received a placebo.

In all, 64 HIV infections were recorded among the 1,248 study participants who received a placebo pill, while 36 HIV infections were recorded among the 1,251 participants who received the study drug. The average reduction in HIV infection risk of 43.8% includes all study participants – even those who did not take the daily pill consistently.

The iPrEx study found that PrEP was more protective among those who reported taking the pill more regularly. Among participants who used the tablet on 50% or more of days, as measured by pill counts, bottle counts and self-reports, risk of HIV infection fell by 50.2% (95% CI 17.9-69.7%; P=0.006); among those who used the pill on 90% or more of days, as determined by the same measures, the PrEP pill reduced infection risk by 72.8% (95% CI 40.7-87.5%; P=0.001).

While pill-taking measures that rely on self-reports are not objective, testing to measure levels of the PrEP drug in the blood of study participants - a more reliable measure of pill-taking - also indicated that those participants who were protected against HIV infection were likely taking the study drug more regularly. Among a subset of study participants who received the active drug, detectable levels of the PrEP drug combination were found in the blood of 51% (22 of 43) of a group that remained HIV-negative, but in only 9% (3 of 34) of participants who became HIV infected. Low or absent drug levels underlay all of the infections that occurred among those who received active PrEP, while those who used the drug more regularly had higher levels of protection against HIV infection.

"The iPrEx study proves that PrEP provides important additional protection against HIV when offered with other prevention methods such as HIV testing, counseling, condom use and management of sexually transmitted infections," said iPrEx Protocol Chair Robert Grant, MD, MPH of the Gladstone Institutes and the University of California at San Francisco. "As with other prevention methods, the greatest protection comes with consistent use. I hope this finding inspires a renewed commitment from communities, industry and government to stop the spread of HIV."