Study results announced Feb. 24 by the French national HIV research agency ANRS at the Conference on Retroviruses and Opportunistic Infections ( CROI ) in Seattle suggested that a three-day regimen of the Pre-Exposure Prophylaxis, or PrEP, intervention reduced HIV risk significantly in men who have sex with men ( MSM ) by an average of 86 percent.
PrEP is usually available in the form of the pill Truvada, manufactured by Foster City, California-based Gilead Pharmaceuticals. The pill, initially developed as an HIV medication, has been approved for use as PrEP in the United States since 2012. The standard dosage has been taking one pill daily. Previous studies have shown that adhering to that regimen have reduced the risk of infection by over 90 percent.
But the French study suggested that one pill taken 2-24 hours before a sexual encounter, another 24 hours after the encounter, and then another 24 hours after that, may be nearly as effective. The study, implemented in France and Montreal, began in 2012 and was discontinued in late-2014 because of high efficacy. About 400 subjects took part in the study.
Officials of the Centers for Disease Control and Prevention lauded the findings in a Feb. 24 statement.
"We applaud ongoing efforts like IPERGAY to identify PrEP dosing strategies that may be more acceptable than oral daily dosing for some individuals at risk, and could potentially lower costs," said the statement. "In addition, researchers are working to identify alternative delivery vehicles, including injectable PrEP and insertable products, such as a vaginal ring. These are exciting avenues for research."
At the same time, however, they cautioned that a great many unanswered questions remain about the strategy, such as whether it would be applicable to heterosexual men and women, or IV drug users. Furthermore, they said data would be needed to see how well such a complex strategy could be carried out outside a trial setting.
Researchers also would need to determine how long it takes to build up an optimal amount of PrEP in the bloodstream in order to provide maximum protection against infection, especially for individuals who do not engage in sexual activity frequently. Individuals who have sexual relations several times a month would presumably have a higher amount of PrEP in their bloodstream should they adhere to the regimen; findings have shown high levels of protection for individuals who take PrEP at least four times weekly. Men in the IPERGAY study were taking PrEP, on average, three to four times a week.
"CDC continues to recommend only daily use of PrEP, as approved by the FDA. IPERGAY findings combined with other recent research suggests that even with less than perfect daily adherence, PrEP may still offer substantial protection if taken consistently," its statement said.
Also at CROI, researchers from the U.K. Medical Research Council, on Feb. 24, presented the results of the PROUD open-label study, which found that daily oral PrEP using Truvada reduced risk among MSM in that study by 86 percent as well.