How soon is PrEP effective after a break of a week?

Question

I was on prep for 30 days and missed prep doses for a week. I did not have any sex during that time. However I am back on prep and I have had 4 doses after my one week break. My question is when will prep become fully effective after this break in order for it to be safer to have unprotected anal sex again.

Answer

For all intents and purposes, after missing a week of PrEP and restarting, it will be just like you are starting the first time since there is currently no drug in your system. However long it took for you to become effective the first time is how long it will take you now after a one week break.

Exactly how long it will take for you to build maximal protection depends on who you ask and where you ask it. Dr. Dave Glidden has demonstrated that there is about 77% protection for rectal sex even after one dose (http://www.aidsmap.com/Intermittent-PrEP.../page/2986809/). The French IPERGAY trial has shown maximal protection is offered for rectal sex when 2 doses are used 2-24 hours before a sexual event, then one dose 24 hours later, and another 48 hours after that (http://www.aidsmap.com/Ipergay-trial-PrEP-still-protected-people-who-had-less-sex-and-used-it-less-often/page/3159786/). The U.S. CDC says that PrEP reaches maximum protection from HIV for receptive anal sex at about 7 days of daily use. For receptive vaginal sex and injection drug use, PrEP reaches maximum protection at about 20 days of daily use (https://www.cdc.gov/hiv/basics/prep.html).

So as you can see, no matter which framework we're using, four consistent doses appear to offer significant prophylaxis for anal sex. In that case you are definitely having protected anal sex, not "unprotected" anal sex as you asked. PrEP, with or without condoms, offers protection for anal sex of 99% or greater when taken as prescribed. It is safe to say that after four consistent doses you are having protected anal sex.

You don't mention why you took a week break, if this was planned, or by choice. But in any event, I hope this information helps you to make sexual decisions that allow you to have the kind of intimacy and pleasure you wish to experience.