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Difficulties with on-demand PrEP highlighted by two studies

Hester Phillips

27 July 2023

West African and USA studies involving men who have sex with men found most had problems predicting sex and some struggled to take post-sex pills

Portrait of mid 20s African-American man outdoors at dusk
Photos are used for illustrative purposes. They do not imply health status or behaviour. Credit: xavierarnau

Two studies into on-demand PrEP use among men who have sex with men suggest the majority are likely to encounter difficulties with taking it and would still be at risk of HIV. 

What is the research about? 

The West African study involved around 650 men who have sex with men (ages 18+) and took place in Burkina Faso, Côte d’Ivoire, Mali and Togo. The USA study involved 120 young men (aged 16-24) who have sex with men. 

Both assessed some aspect of on-demand PrEP. This is when you take two PrEP pills between 2 to 24 hours before having sex, then one PrEP pill after 24 hours of the first dose, and one after 48 hours (sometimes referred to as ‘2-1-1’). On-demand PrEP is an alternative to daily PrEP (when you take one pill every day for as long as you are at risk of HIV). 

Why is this research important? 

Not everyone who wants to take PrEP wants to take it every day. But how effective on-demand PrEP is depends on whether people can predict when they are going to have sex so they can take the first pill in time, and whether they remember to take the second two pills.  

What did they find out? 

USA study 

Over an eight-week period, participants were asked to predict whether they were going to have sex in the next 24 hours and report on any sex they had.  

More than two-thirds (69%) of participants had at least one unpredicted sexual encounter during the study. Had these men been using on-demand PrEP they would not have been protected.  

Participants also reported high-risk behaviours: 

  • 73% of sex acts were condomless 

  • 32% were with a stranger 

  • 29% involved alcohol or drugs. 

West African study 

This study gave participants a choice between on-demand and daily PrEP then tracked adherence and HIV infections. 

On-demand PrEP was the most popular choice. It was chosen in 72% of cases. Daily PrEP was chosen in 26% of cases, and PrEP was stopped in 2%. 

When assessing adherence, researchers found that only 44% of sex acts among participants using on-demand PrEP were sufficiently covered by the PrEP doses to protect against HIV infection. For people taking daily PrEP, 74% of sex acts were covered. 

Twenty-five people got HIV during the study. Of these, 21 were using on-demand PrEP, 2 were using daily PrEP and 2 had stopped taking PrEP for several months. 

Overall HIV incidence was 2.0 per 100 person-years. This is one of the highest incidence rates of any PrEP study involving men who have sex with men. HIV incidence was 4.4 times higher for participants using on-demand PrEP than daily PrEP (2.4 per 100 person for event-driven PrEP, 0.6 per 100 person-years for daily PrEP, and 7.9 per 100 person-years for no PrEP). 

Only two men who got HIV had detectable levels of PrEP in their blood. One of these men had developed resistance to PrEP due to poor adherence. 

Some of the men who got HIV during the study were interviewed. They said sex sometimes occurred at a moment’s notice so they were unprepared.  

Those who had been able to predict sex, sometimes found it difficult to remember to take the second two pills. Adherence problems were linked to side effects or changes in routine caused by work, travel or alcohol use.  

Although some participants used PrEP inconsistently, they did not always start using condoms.  

What does this mean for HIV services? 

Many men who have sex with men may find it challenging to take on-demand PrEP. It is important to provide clear information and non-judgemental counselling so that individuals fully understand what each PrEP regimen requires and which is likely to suit their lifestyle.  

For men who have sex with men who frequently have condomless sex and/or find it difficult to predict when they are going to have sex, daily PrEP is likely to be more effective. 

Men who have sex with men who choose on-demand PrEP should receive support to help them take it correctly. This could involve providing tools and support to help individuals better predict when they are likely to have sex. It could also involve providing dosing reminders via text message or Whatsapp.  

There is also a need to encourage men who have sex with men to use condoms. Particularly if they are using on-demand PrEP but have not been able to take it in time to protect themselves. 

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