Daily PrEP use, rather than on-demand dosing, may be better for young MSM due to their inability to predict sexual encounters accurately and consistently.
“Young MSM (YMSM) account for almost a quarter of new HIV diagnoses in the United States each year,” Bryce Stamp, MPH, notes. “Historically, uptake of PrEP among YMSM has been low, and many YMSM who are prescribed PrEP struggle to take a pill daily, despite their risk for HIV.”
As a result, the use of alternative dosing strategies, including on-demand PrEP, may be of benefit for individuals who struggle to take, or are uncertain about taking, PrEP daily. “In this ‘on-demand,’ or ‘2-1-1’ strategy, two pills are taken 2 to 24 hours before sex and a single dose is taken at both 24 and 48 hours after sex, meaning that YMSM must be able to predict that they’re going to have sex far enough in advance to start the dosing cycle,” Stamp says.
However, little is known about the ability of young people to predict sex 2 to 24 hours in advance. For a study published in JAIDS, Stamp and colleagues aimed to address this research gap. They assessed 120 YMSM (median age, 21; 47.5% White) for 8 weeks through digital daily surveys to measure engagement in and prediction of anal sex over 24 hours, as well as condom use and other encounter-level factors. An unpredicted spontaneous sexual encounter, which the researchers defined as an anal sex encounter that took place without “sufficient prior knowledge” to hypothetically enable the use of on-demand PrEP, served as the primary outcome.
Few YMSM Predict Sex Well Enough for On-Demand PrEP
About half the study population (46.6%) reported their relationship status as single, and 18.6% stated that they were “casually dating.” More than half of the participants (58.3%) had never taken PrEP.
“In total, 108 of the 120 participants reported a total of 845 anal sex encounters and 952 anal sex acts (insertive/receptive) during the study period,” Stamp says (Figure). “Encounters were distributed fairly evenly across partner types (main, casual, anonymous); however, 41% of encounters with an anonymous partner would not have been protected (hypothetically) by on-demand PrEP use. Overall, 73% of sexual acts were condomless, and approximately 30% of sexual encounters involving condomless sex would not have been protected by hypothetical on-demand PrEP use. Condoms were more likely to be used when there was less planning/prediction of sex in advance.”
These findings highlight the difficulties of on-demand PrEP use in this population, Stamp says. “Given that as many as one-third of encounters were unpredicted and spontaneous, and that two-thirds of participants had such an encounter in an 8-week period, it appears that YMSM may struggle to predict/plan for sex in ways that would allow good protection with on-demand PrEP.”
Understanding Best PrEP Strategies
For YMSM who have frequent sexual encounters or have difficulty predicting them, daily PrEP use in combination with adherence support may be the best HIV prevention strategy, according to Stamp.
“Those who have less frequent sex, or those who may have a better understanding of when sexual encounters are likely to occur, may be candidates for this dosing approach, so understanding patients’ frequency of and ability to plan sex is necessary when discussing PrEP dosing strategies,” he says.
Stamp notes that the study examined whether YMSM’s ability to predict sex was hypothetically adequate to allow for on-demand PrEP use based on dosing cycle guidelines; it did not examine whether participants actually started a dosing cycle if they thought they would have sex in the next 2 to 24 hours. “Therefore, future work is needed to assess actual pill-taking and adherence to an on-demand regimen among this age group,” he says. “Our group is examining relationships between patient characteristics and prediction of sex, with the idea that understanding these relationships may allow for identification of YMSM in whom on-demand PrEP strategies are most likely to succeed.”
