Post-exposure prophylaxis

Overview
Post-exposure prophylaxis (PEP) is any prophylactic treatment started immediately after exposure to a disease (such as a disease-causing virus), in order to prevent the disease from breaking out.

PEP is commonly used, and very effective, to prevent the outbreak of rabies after a bite by a rabid animal. The treatment consists of repeated injections of rabies vaccine and immunoglobulin.

In the case of HIV infection, post-exposure prophylaxis is a course of antiretroviral drugs which is thought to reduce the risk of seroconversion after events with high risk of exposure to HIV (e.g. unprotected anal or vaginal sex, needlestick injuries, or sharing needles). To be effective, it must be started as soon as possible after exposure and ideally within an hour. The treatment for HIV lasts four weeks.

While there is compelling data to suggest that PEP after HIV exposure is extremely effective, there have been cases where it has failed. The regimen can be very demanding and have unpleasant side effects including malaise, fatigue, diarrhoea, headaches, nausea and vomiting.

According to one Australian study, two thirds of people taking PEP experienced mild to moderate side effects and one quarter of people taking PEP experienced severe side effects.