Q and A


I missed my timings with on-demand PrEP dosing, should I start PEP?

I am a gay man and I use on demand PrEP, but I was a bit late with my first single dose after my initial double dose. I was wondering if I am in bad shape and need PEP. To be specific, I took the initial double dose and I had unprotected insertive anal sex 30 hours after that. I took my first single dose 36 hours after the initial double dose. Then I took my second single dose 48 hours after the initial double dose.


Hi, how are you?

No you do not need to take PEP.

The initial double dose affords you some protection as the higher dose remains in your body longer than 24 hours. This should extend to the 36 hours post the double dose for when you took your next dose. Your final dose was at the right time so this does change anything further.

In general it is best to take the double dose no more than 24 hours before sex. This is when the concentration is highest and offers the best protection. At 30 hours there will still be protection, but not as high as seen in studies demonstrating 24 hour effectiveness.

From this first dose, the subsequent single dose is 24 hours after and the final 24 hours after that. While being closer to the timings help improve the effectiveness, taking PrEP at a less than ideal time will still give more protection than no PrEP. Example of on demand dosing. 



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