Question
Will 2:1:1 PrEP dosing be okay if the last dose is a little late?
9 October 2026. Related: Adherence, All topics, PEP/PEPSE.
Question: Hi, I’m worried about whether I’ve taken the 2:1:1 prep correctly so I hope someone can help please.
7th Oct 2 pills at 9am
7th Oct unprotected sex as insertive and receptive at 1:30pm
8th Oct 1 pill at 9am
9th Oct 1 pill at 1:30pm (4.5 hours late)
Do I need to be considered about the last pill?
Thanks
Answer
Hi there
Yes, this should be fine.
Dosing doesn’t have to be exact, especially after starting with the double dose,
Drug levels will still be good, even if you are a few hours early or late with the following doses.
If you are worried, just take a final dose the next day too – ie 2:1:1:1.
You don’t need to do this, but the extra dose would be very safe if it makes you feel better.
Please see this guide for more info:
i-base.info/guides/prep
Hi Roberto, you already asked this question before and the answer is the same. This i-Base service isn’t set up as either an emergency service, or run by people who can prescribe PrEP. However, the double dose when starting PrEP generally gives very high levels of protection though that cover the following doses being a bit late.
You are not describing a high level of risk. UK guidelines would be unlikely to recommended needing PEP.
Please realise that there is no data on the impact of slightly late or early doses because even in research studies this level of detail for events that happened months earlier is never available.
Hi Experts,
I would appreciate your advice on whether PEP is necessary following a possible error with my 2-1-1 on-demand PrEP schedule.
Here is my timeline:
Saturday, October 10, approximately 5:30 PM: I took 2 tablets of TDF/FTC (Truvada equivalent), at least 4 hours before my first sexual encounter.
Sunday, October 11, approximately 1:00 PM: I may have taken the scheduled follow-up tablet, but I cannot remember with certainty because I was intoxicated/hungover.
Sunday, October 11, approximately 11:30 PM: Because I was unsure whether I had taken the previous dose, I took 2 additional PrEP tablets, approximately 30 hours after the initial double dose.
I also had additional sexual encounters the following morning.
My exposures included:
Brief condomless receptive anal intercourse without ejaculation.
Anal intercourse with condoms.
Oral sex while I had a small aphthous ulcer in my mouth.
Sharing a dildo.
My main concern is that I may have missed the 24-hour follow-up dose and only taken additional tablets approximately 30 hours after the initial dose.
I have already started Biktarvy as PEP because I was concerned about the possibility of inadequate PrEP protection. I have also scheduled an appointment with an HIV specialist.
My questions are:
Would the initial double dose, taken at least 4 hours before sex, plus the additional tablets at approximately 30 hours, still provide adequate protection?
If I missed the 24-hour tablet, does this constitute a significant enough lapse to warrant PEP?
Given these circumstances, would you recommend completing a full 28-day PEP course?
I understand that individualized medical advice is important, but I would greatly appreciate your perspective on the level of risk and the relevant PrEP guidelines.
Thank you very much for your help.
Hi Sam, for this example, the timing isn’t really important and won’t make any difference.
Hi Simon,
I really do appreciate your quick reply.
In regards if I was to take another one tomorrow for a peace of mind, would that be the original time at 9am or 1:30pm (24 hours from today’s dose).
Thank you