Question
Am I taking on-demand PrEP correctly?
25 November 2023. Related: Adherence, All topics, PrEP.
Hello, I was advised by my doctor to take the PrEP 24 hours in advance of sex for on-demand use. But I think I may taking it incorrectly. I’ve been taking the first 2-pills 24 hours in advance, followed up by the second dose at 24 hours (after taking the first 2-pills) and then having sex after giving a bit of time for the second dose to be absorbed. I then follow with the standard 3rd and 4th doses 24 and 48 hours later. But wondered if the prep is still effective if I’m having sex just outside the first 2-24 window, or if it should really be within that window for maximum effectiveness? Additionally, would it be ideal to have the second dose at least 2 hours before sex, even if you took the first 2 pills 24 hours in advance?
Answer
Hi, how are you doing?
The first dose of on-demand PrEP is recommended to be taken 2-24 hours before having sex.
You do not need to take the second dose before sex to increase how effective it is going to be.
How you have been taking it is also suitable, it is more akin to daily dosing. After starting with the on-demand double dosing, you can continue taking it daily and it will still be effective regardless of when you have sex.
The most important part is to continue with PrEP for 2 days after having sex regardless of how you are taking it.
As long as you have taken a double dose of on-demand PrEP at least 2 hours before sex it will be effective.
Josh.
Hi Luis, the references used for the UK Guide to PrEP include the French/Canadian IPERGAY and PREVENIR studies, These showed that 2:1:1 dosing was just as effective as daily PrEP in gay men.
https://i-base.info/guides/prep
https://i-base.info/guides/prep/references
Many other studies, including iPrEX reported on the effectiveness of taking at least four doses a week.
Everyone is now recommended to start PrEP with a double dose, which will make 4 doses a week even more solid.
I’ve read that daily PrEP is up to 99% effective, but I haven’t been able to find concrete data on the effectiveness of PrEP on-demand or if taking at least 4 doses per week provides similar protection than daily PrEP. Could you provide more information on this, currently I use PrEP on-demand. Thanks.