72 Hours for PEP. Is it sooner better?


I've read some people (even on this site) say PEP can be started anytime within 72 hours and it doesn't make a difference when.

But in a SF study, they found that all success of PEP had a median start time of 33 hours and all failures had a median time of 55 hours. This would suggest that starting early is better.

I know people aren't monkeys, but the animal study showed that all monkeys started on PEP on hour 24 were not infected, All monkeys who started at hour 48 failed. (Well one seem to pass, but later became positive).

The NY City has update it's guidelines to say PEP should be started within 36 hours. Although, they leave up to the patient and physician to decide if it can be started after 36 hours.

What are your thought? Is there a better study?


Hello and thanks for posting your interesting question.

I'm not sure if that's exactly what I said. The usual recommendation is that PEP should be started within 72 hours of exposure.

It makes biological sense to start it as soon as possible (I was perhaps lucky to start on PEP about 20 minutes after a large hospital exposure.) This is not a time to dawdle. The problem is that the studies are all too under powered to draw definitive conclusions about the relative benefits of starting at this hour or that.

My usual suggestion is that PEP should be started as soon as possible after the exposure, but certainly before 72 hours. BY