Here’s why PEP is taken for 28 days

Credit: Dr. William Valenti

Someone asked the other day about why is it necessary to take post-exposure prophylaxis for 28 days. The person had heard that PEP meds were hard on the liver and immune system, and so 28 days seems like a long time.

This is a good Sexual Health question. Most of the science behind the 28-day recommendation comes from animal studies and small studies of health care workers who did not complete the 28-day course of treatment.

HIV attaches to human cells depending on the amount of virus entering the body after a sexual encounter. HIV also attacks different parts of the body on different schedules -- sometimes taking as long as a week to attach completely.

The goal of PEP is to kill virus and stop its attachment to cells. This works best if PEP is given as soon as possible after condomless anal sex; with best results when PEP is started within 72 hours of exposure.

The 28-day schedule is used to give PEP the best chance of working, and 28 days is considered short-term.

After more than 20 years of giving PEP, I’ve found that most side effects are stomach upset that lasts a few days, then goes away. Liver problems can happen occasionally, and we look for this with blood testing before starting and at the end. If needed, we can check blood during the 28 days of treatment.

The other good news is that the drugs used for PEP, PrEP and HIV treatment attack HIV without doing harm to the immune system. In fact, when used for treatment, HIV drugs improve the immune system by clearing virus and restoring T-cell numbers.

The article that I suggest is a long discussion, but answers all the questions - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4216036/

Check out a shorter version from CDC - https://www.cdc.gov/hiv/basics/pep/about-pep.html