How Effective Is PEP?

Post-exposure prophylaxis (PEP) involves taking anti-HIV medications immediately after any potential exposure to HIV
Post-exposure prophylaxis (PEP) involves taking anti-HIV medications immediately after any potential exposure to HIV

Post-exposure prophylaxis (PEP) involves taking anti-HIV medications immediately after any potential exposure to HIV (human immunodeficiency virus) to prevent HIV infection (acquired immune deficiency syndrome or AIDS). PEP may prevent HIV from entering the cells in the body and stop someone from getting an HIV infection. However, there is no guarantee that a person exposed to HIV will not become infected with HIV after taking PEP. PEP should be used only in emergencies after exposure to HIV. It should not be used as a replacement for or HIV prevention methods.

PEP normally consists of three anti-HIV drugs from the different drug classes. The most recent guidelines recommend using Truvada (a fixed-dose combination tablet combining emtricitabine and tenofovir) and Isentress (raltegravir) from the integrase inhibitor class.

Effectiveness of PEP

The important things that need to be followed for PEP to work effectively include:

  • PEP must be started within 72 hours of possible exposure to HIV for it to be effective.
  • It works best if PEP is taken within 24 hours of being exposed to HIV.
  • Medication must be taken as advised, regularly every day for 28 days (4 weeks course).
  • Drug levels must remain high during the month of treatment to help prevent infection. (Irregular medication will lower the drug levels in the body.)

The PEP treatment will not be effective if:

  • The medicines are taken irregularly or incorrectly.
  • The medicines are not taken soon enough, which is within 72 hours after potential exposure to the virus.
  • The full course of PEP drugs is not completed.
  • Further exposures to HIV happen while taking PEP.

What is the role of PEP in the prevention of HIV?

Once HIV enters the body, they infect certain immune cells and replicate within these immune cells. Then, it spreads throughout the body causing HIV infection. PEP works by interfering with this pathway that HIV uses to cause infection in the body. The anti-HIV drugs get into the bloodstream and tissues. This prevents HIV from replicating within the body’s immune cells.

The medicines used in PEP are called antiretroviral medications (ART). These include tenofovir, emtricitabine (these two drugs come in one pill), and a third drug either raltegravir or dolutegravir. These medications prevent HIV from making copies of itself and spreading through the body.

PEP involves using the combination of the three HIV medications, which are taken two to three times a day for 28 days, to reduce the risk of getting HIV infection after a potential exposure to HIV. PEP is effective in preventing HIV infection when it’s taken correctly, but it’s not 100% effective. PEP can lower the risk of getting HIV infection by more than 80%.


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When is PEP necessary?

PEP must be taken by a person soon after a known or doubted exposure to HIV to prevent HIV transmission.

Incidences of known or doubted exposure to HIV includes:

  • Unprotected sex (without using a condom) with someone whose HIV status is not known or who is HIV-positive.
  • Condom breaking during sex.
  • Sexual assault.
  • Drug users, sharing needles or other injecting equipment with someone who may have HIV.
  • Occupational PEP: After exposure to HIV material at work (health care).
  • Getting blood or other body fluids that may have HIV in the eyes, mouth, or on the skin.
  • A child born to an HIV-positive mother.

What are the side effects of PEP?

PEP is safe. The side effects caused are not life-threatening and can be treated. PEP may cause the following side effects in some people:

Centers for Disease Control and Prevention. Post-Exposure Prophylaxis (PEP). Post-Exposure Prophylaxis. U.S. Department of Health & Human Services.

Markelz AE. Postexposure HIV Prophylaxis in Physicians and Medical Personnel. Medscape.