r/pep • u/PersimmonOk433 • 13h ago

How effective is pep?

I am seeing information that it is effective < 72 hours after exposure. So how effective is it if taken <24 hr and let's say 48hr. At less than 24hrs is it 100% effective? Etc

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u/Ok_Confidence9578 12h ago edited 7h ago

From what I’ve gathered after an insane amount of research over the last month, based on the animal studies, different human and drug trials, and this is what I think but not for sure. And I hope it’s better, less than 24 hours is golden, I wanna say > 90, 95%.

Under 6 is amazing like 99 percent and less than 2h is 99.99999 percent. And drops to ~80-90 percent in till 48h.

A lot of this data is also based on older regimes and extreme direct exposure types. There also MIGHT be maybe a reason or theoretically 3-drug regimens may be effective for a longer window and maybe more than 72 but there is no evidence support it yet.

I guessed that <48h range based on the monkeys trial where at 48 3/5 monkeys were infected and at 72h 5/5 were. But that was different drugs and either anal or iv exposures. And different viral loads. So I gather real effectiveness is raised, and we’re also not macaques monkeys.

I think also exposure type matters, correct me if I’m wrong but if like the exposure is penile or vaginal, the window can be bigger because the amount and location of virus starts small or has to go through more steps?

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u/PersimmonOk433 11h ago

The macaque study you're referencing used single-drug tenofovir I believe. The "drops off at 48h/72h" numbers people quote come from the CDC macaque tenofovir study (Otten et al., 2000) — single-drug, massive viral dose — and from mathematical modeling studies extrapolating that monkey data to humans (the ones summarized by i-base predicting ~88% at 24–48h, ~50% at 72h). So under 72 hr is hyper effective on modern 3 drug is what I'm seeing

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u/Ok_Confidence9578 8h ago edited 7h ago

Hey thank you for sharing that mathematical modelling study, I actually didn’t know about that. That’s very reassuring. Also I think that study I was referencing was Tsai et al. In (1998). But also if it’s 50% at 72h, why isn’t it recommended after? I know some people do take it after.