HIV in Canada: A primer for service providers

Post-exposure prophylaxis (PEP)

Key Points

  • PEP reduces the risk of HIV transmission by between 80% and 90%.
  • Post-exposure prophylaxis (PEP) is the use of antiretroviral drugs after an actual or suspected exposure to HIV to prevent HIV transmission.
  • PEP works by helping to prevent replication of the HIV virus once it has made its way into the body.

Post-exposure prophylaxis (PEP) is the use of antiretroviral drugs after an actual or suspected exposure to HIV to try to prevent HIV transmission. It should be started as soon as possible after a real or suspected HIV exposure but definitely within 72 hours. A combination of two or three antiretroviral drugs is generally prescribed for PEP use. These medications must be taken every day for four weeks.

PEP works in an HIV-negative person after HIV has made its way into the body. If this happens the medications in PEP may prevent the virus from multiplying and spreading throughout the body.

There is evidence that suggests providing PEP after a potential exposure to HIV can help reduce, but not eliminate, a person’s risk of HIV infection. First, in monkey studies, taking PEP for one month protected almost all of the monkeys against infection by HIV-like viruses. Second, two studies that compared the number of HIV infections in people who took PEP with the number of infections in those who did not take PEP provided evidence that taking PEP may reduce the likelihood of HIV transmission after a recent exposure by between 80% and 90%.

Factors that can limit the effectiveness of PEP include: poor adherence to daily pill taking for the full four-week course, longer time to PEP initiation, and continued exposures to HIV while taking PEP (PEP is only meant to reduce the risk from a single exposure).

The potential risks of PEP include drug toxicity and side effects, interactions with other medications and the development of drug-resistant strains of HIV (if infection occurs). A person who wants to use PEP will have their HIV risk assessed. This therapy is only meant to be used after a potential high-risk exposure. Also, an HIV test will need to be performed to confirm that the person is HIV negative before starting PEP.

PEP should be combined with a comprehensive sexual health plan that includes regular STI testing and treatment and ongoing adherence and risk-reduction counselling to reduce the risk of the sexual transmission of HIV.


Post-Exposure Prophylaxis for Prevention (PEP)

Post-exposure Prophylaxis (PEP) – CATIE fact sheet

Can we prevent infection with HIV after an exposure? The world of post-exposure prophylaxis (PEP)Prevention in Focus

The PEP Program at Clinique l’Actuel Programming Connection

Updated Guidelines for Antiretroviral Postexposure Prophylaxis After Sexual, Injection Drug Use, or Other Nonoccupational Exposure to HIV—United States, 2016 – U.S. Centers for Disease Control and Prevention (CDC)



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