Pre-exposure prophylaxis, or PrEP, typically is prescribed as a daily regimen: A single pill comprised of tenofovir disoproxil fumarate plus emtricitabine is swallowed each day to provide maximum protection against HIV infection. Recent research focused on obviating the need for daily dosing has revealed that dosing based around the frequency of sexual activity
provides adequate protection for men vulnerable to HIV infection.
Investigators set out to learn whether this remains true for men who engage in less frequent sex, who would therefore take less frequent doses of PrEP. The results were published in The Lancet HIV
The investigators running France’s ANRS IPERGAY trial, a double-blind study which confirmed that on-demand PrEP reduced HIV risk in sexually active men, analyzed data on 400 subjects who took part.
The subjects had been randomized to receive either PrEP or a placebo. Out of the 400 subjects, 270 reported at least 1 episode during which they were less sexually active (a median of 5 instances of sexual activity per month) but still adhered to their on-demand PrEP regimens. The on-demand regimens consisted of 2 pills anywhere from 2 to 24 hours before having sex, another pill 24 hours after the first 2, and a final pill 24 hours after that.
Because this was a multiyear study, the investigators counted time in person-years, with a total of 431 person-years measured for the 400 participants. In 134 out of 180 person-years in which participants said they took 15 or fewer pills monthly, participants indicated that they used the pills systematically in accordance with their sexual frequency. In this group, none of the participants who were given PrEP contracted HIV, while 6 who took the placebo as directed eventually were diagnosed with the virus. This translated into an incidence rate of 9.2 per 100 person-years in the placebo group compared with zero who were given PrEP.
“In this [IPERGAY] analysis, we observed an RRR [relative risk reduction] of 100% with an average uptake of 2.2 pills per week, provided that adherence to the on-demand PrEP regimen was high,” the authors wrote in the discussion section of their report. “Our results provide evidence of high efficacy of on-demand PrEP for less frequent episodes of sexual intercourse.”
These results support those of previous studies
in this area, including those involving macaque monkeys who were protected after being given intermittent PrEP based on rectal exposure to HIV. Another study
found a sufficiently protective concentration of PrEP drugs in colorectal tissue in healthy women after they took the pills just twice a week.
The investigators noted that because patients were asked to report their own sexual activity and pill taking, it is impossible to guarantee that reported timing of these events is precise. In addition, the study was unable to determine whether on-demand PrEP is protective for people who engage in sex very rarely; further studies should be able to shed light on this question.
Overall, the research team feels that event-driven PrEP is a solid alternative to daily pill taking for high-risk men. “The choice of a daily or on-demand PrEP regimen should be offered to men who have sex with men, including individuals who have less frequent sexual intercourse, provided that they maintain high adherence,” they wrote.
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