On demand PrEP effective for gay men having less frequent sex

09 January 2020

Findings from France and Canada suggest it is safe to offer men who have sex with men a choice between daily and ‘on-demand’ PrEP if they are not having frequent sex.

Shirtless man holding a PrEP pill

The study is part of the ANRS IPERGAY trial, which previously found that ‘on-demand’ pre-exposure prophylaxis (PrEP), whereby someone takes antiretrovirals before and after sex, was associated with an 86% reduction of HIV incidence among men who have sex with men engaging in high frequencies of condomless sex. However, the effectiveness demonstrated by the trial might have been due to the fact that participants were taking a high volume of on-demand doses. It is estimated that men taking four doses of PrEP or more a week could result in an accumulative effect similar to taking PrEP on a daily basis.

The current study set out to address this knowledge gap by investigating whether on-demand PrEP remained effective for men who have sex with men who were having less frequent sex and were therefore taking fewer on-demand PrEP doses.  

A total of 400 people took part in the study, which was conducted between 2012 and 2014. Half were given PrEP (a fixed-dose combination of tenofovir disoproxil fumarate and emtricitabine) and half a placebo pill. Participants were from France or Canada and were either men who have sex with men or transgender women who have sex with men. All participants engaged in condomless anal sex.

Participants were given a supply of pills – either PrEP or the placebo – each month and were told to take two pills between 2 and 24 hours before sex, a third pill 24 hours after taking the first dose, and a fourth pill 24 hours later. For prolonged episodes of sex, participants were instructed to take one pill per day until the last sex act then take two pills.

After enrolment, participants were followed up each month for two months then every two months after that. Pill uptake was assessed by counting returned pills at each follow-up visit and by estimating tenofovir concentration from frozen plasma samples. Participants were also interviewed about their pattern of sex and PrEP use.

A total of 270 participants, roughly half in each group, had at least one period of less frequent sex during the study, defined as taking a maximum of 15 pills per month. During these periods, participants reported a median of 5 episodes of sex per month and used a median of 9·5 pills per month.

On-demand PrEP was found to be highly effective among those having less frequent sex. During these periods, the HIV incidence rate in the placebo group was 9·2 per 100 person-years – or a total of six HIV infections – compared to no infections among those taking PrEP, giving a relative reduction in HIV incidence of 100%.

These results suggest men who have sex with men could safely be offered the choice of altering their PrEP intake, taking on-demand PrEP during periods of less frequent sex. Due to its small sample size the current study could not evaluate how effective on-demand PrEP is for men who have sex with men having sex at an even lower frequency, such as once a month, and is therefore something other PrEP trials should consider investigating.

Written by Hester Phillips

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