HIV in Canada: A primer for service providers


Post-exposure prophylaxis (PEP)

Key Points

  • Post-exposure prophylaxis (PEP) is the use of antiretroviral drugs after an exposure to HIV, to reduce the risk of HIV transmission.
  • PEP works by helping to prevent replication of HIV after it has made its way into the body.
  • PEP can reduce the risk of HIV transmission by over 80% when used consistently and correctly.
  • PEP is meant for emergencies only.

Post-exposure prophylaxis (PEP) is the use of antiretroviral drugs after an actual or suspected exposure to HIV to reduce the risk of HIV transmission. It should be started as soon as possible after a potential HIV exposure but definitely within 72 hours. A combination of three antiretroviral drugs is generally prescribed for PEP use. These medications must be taken every day for four weeks, and a person should have no further exposures to HIV during this time.

PEP works in an HIV-negative person after HIV has entered the body. If HIV is in the body, the medications in PEP can prevent the virus from multiplying and spreading throughout the body and causing a permanent infection.

Research has found that PEP can reduce the risk of HIV infection by over 80%. In those studies PEP was not always used consistently and correctly, so this number is likely much higher when PEP is used as intended. Factors that can limit the effectiveness of PEP include: low adherence to the full four-week course of pills, later PEP initiation, and continued exposures to HIV while taking PEP (PEP is only meant to reduce the risk from a single exposure).

PEP is generally well tolerated and associated with minimal side effects. Other potential risks of PEP include drug toxicity, interactions with other medications, and the development of drug-resistant strains of HIV (if infection occurs while the person is taking PEP). A person who wants to use PEP will have a risk assessment conducted by a healthcare provider, because PEP is only recommended for use after a potential high-risk exposure. They will also be tested for HIV to confirm that they are HIV negative.

PEP is meant for emergencies only and is not intended for people with ongoing exposures to HIV. People who engage in high-risk behaviours on a regular basis, or who find themselves using PEP frequently, should consider using pre-exposure prophylaxis (PrEP) to prevent HIV instead.


Post-Exposure Prophylaxis for Prevention (PEP)

Post-exposure Prophylaxis (PEP) – CATIE fact sheet

Canadian guideline on HIV pre-exposure prophylaxis and nonoccupational postexposure prophylaxis

HIV Post-Exposure Prophylaxis (PEP) Guidelines – British Columbia Centre for Excellence in HIV/AIDS

Alberta guidelines for post-exposure management and prophylaxis: HIV, Hepatitis B, Hepatitis C and sexually transmitted infections –  Alberta Health Services

Guide pour la prophylaxie et le suivi après une exposition au VIH, au VHB et au VHC – Ministry of Health and Social Services of Quebec


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