On-Demand PrEP Still Protective With Less-Frequent Sex

By Anne Harding

December 06, 2019

NEW YORK (Reuters Health) - On-demand pre-exposure prophylaxis (PrEP) is effective for HIV prevention in lower-risk men who have sex with men (MSM), according to a new analysis of data from the ANRS IPERGAY trial.

MSM who had less-frequent sexual intercourse while maintaining high PrEP adherence had a 100% relative reduction in HIV incidence compared with lower-risk men in the placebo group, Dr. Laurence Meyer of INSERM in Villejuif, France, and colleagues report in The Lancet HIV.

"On-demand PrEP (in other terms event-driven) is effective, even in case of unfrequent sex, provided that the subjects take it according to the recommendations," Dr. Meyer told Reuters Health by email.

In the ANRS IPERGAY trial, men on on-demand PrEP with oral tenofovir disoproxil fumarate plus emtricitabine had an 86% reduction in HIV incidence. The on-demand schedule required four pills per act of sexual intercourse. Men had a median 10 sex acts per month, and took a median of 15 pills per month, or roughly four pills per week.

"Therefore, it was unclear whether the reduction in HIV incidence reported in the ANRS IPERGAY trial was because of the repeated uses of four pills per week, which led to enough accumulation of the active drug," the authors explain.

To investigate protection when individuals had sex less frequently, the authors looked at periods during the study when participants took 15 pills or less per month, but did so systematically or often during sexual intercourse, which they classified as high PrEP adherence with less frequent sexual intercourse.

A total of 270 study participants had periods of less frequent sex with high PrEP adherence, totaling 134 person-years and accounting for 31% of the total follow-up time.

This subgroup, which included 134 study participants on placebo and 136 on active treatment, reported a median of five sex acts per month and took a median 9.5 pills per month.

Six patients in the placebo group were diagnosed with HIV during follow-up (9.2 per 100 person-years), while none of the patients in the PrEP group contracted HIV (P=0.013).

"The choice of a daily or on-demand PrEP regimen should be offered to all men who have sex with men, including those who have less-frequent sexual intercourse, provided that they maintain high adherence. Missing doses close to sexual activity is riskier than missing other doses," Dr. Meyer said.

"Our study did not have enough power to assess the efficacy of on-demand PrEP in case of very low frequency of sexual intercourse, such as once a month," he added. "Future open studies of on-demand PrEP will help to clarify the efficacy of on-demand PrEP for single or very rare exposures, or when fewer than 15 pills per month are taken repeatedly for several months."

Dr. Jean-Jacques Parienti, a professor of public health and head of the clinical research department and HIV consultant at the Caen University Hospital in Caen, France, wrote an editorial accompanying the study.

The findings show that "on-demand PrEP is effective among MSM with less-frequent sex (i.e. who really had gaps in taking PrEP)," Dr. Parienti told Reuters Health by email. The next step for PrEP is implementation, he added, noting that GPs in France will be able to prescribe free PrEP.

"Also, more data are required for women," he said.

Gilead Sciences helped fund the study. Dr. Meyer and several coauthors report financial ties to the company.

SOURCE: https://bit.ly/2YiIWsZ and https://bit.ly/33Nd5BG Lancet HIV, online November 26, 2019.