(PEP) is a way for a person who may have recently been exposed to HIV to prevent HIV infection. It involves taking anti-HIV medications after a potential exposure to HIV. Anyone who thinks they may have been exposed to HIV should contact their doctor immediately. PEP is not 100% effective.

PEP consists of a combination of two to three anti-HIV drugs that an HIV-negative person who may have been exposed to HIV takes to reduce their risk of HIV infection. PEP should be taken within 72 hours of being exposed to HIV. These prescription drugs need to be taken every day, exactly as directed, for four full weeks.

How dose PEP work?

Post Exposure Prophylaxis is antiretroviral drug treatment that is started immediately after someone is exposed to HIV. The aim is to allow a person’s immune system a chance to provide protection against the virus and to prevent HIV from becoming established in someone’s body. It usually consists of a month long course of two or three different types of the antiretroviral drugs that are also prescribed as treatment for people living with HIV.

The World Health Organization recommends prescribing zidovudine and lamivudine as the preferred regimen, stating that countries are generally advised to use the same regimens as they would for treating HIV. The British HIV Association recommend a combination of drugs called Truvada and Kaletra.

PEP Singapore is part of a growing trend in using antiretroviral medicine as a preventative measure, along with pre-exposure prophylaxis and treatment as prevention.

Efficacy of PEP

Post Exposure Prophylaxis has been studied in animal trials and human trials. The cumulative evidence is enough to suggest that PEP might be effective in reducing the risk of HIV infection. This conclusion is widely recognized and as a result, a number of countries have produced guides suggesting the possible use of post-exposure prophylaxis in both occupational circumstances and non-occupational circumstances. They tend to suggest that, as it is not 100 percent effective, post-exposure prophylaxis should only be used as a very last resort. In cases where PEP is used, there are various factors that can affect its effectiveness.

Delayed initiation

In order for Post Exposure Prophylaxis to have a chance of working, the medication needs to be taken as soon as possible, and within 72 hours of exposure to HIV. Left any longer and it is thought that the effectiveness of the treatment is severely diminished.

Resistant virus

The person who potentially transmitted HIV may have a drug-resistant HIV, which could make PEP ineffective.


It is very important that a person using Post Exposure Prophylaxis takes the treatment correctly as prescribed by their doctor or healthcare worker and adheres to the full 28-day course. Shortfalls in the provision of counseling and prescription of medicines as well as their side effects, have all been cited as reasons for refusal and non-completion of PEP.