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Prophylaxis (PrEP and PEP)

There are some medications that can be used for the prophylactic treatment of HIV. Prophylaxis or prophylactic treatment for HIV involves taking medications to reduce an individual’s risk of getting the virus. PrEP is for individuals who are currently HIV-negative, but who may be at an increased risk of getting the virus. PEP is used immediately after a potential exposure to HIV has occurred, to prevent an exposed individual from getting infected.

What is PrEP?

Pre-exposure prophylaxis (PrEP) involves taking a daily pill to prevent the transmission of HIV. PrEP is intended to be used by individuals who may be at an increased risk of getting HIV, including those who have a sexual partner with HIV or injection drug users. PrEP contains the medications tenofovir and emtricitabine and must be taken consistently each day to maintain its effectiveness.

Truvada for PrEP

One brand name for PrEP is Truvada. Truvada should be used in combination with safer sex and drug-injection practices in order for it to be most effective. When taken as directed, PrEP may decrease the risk of HIV transmission by 92 percent in men who have sex with men, and 90 percent in heterosexual couples. PrEP may reduce the risk of HIV transmission in individuals who inject drugs by 70 percent, and in all situations, these numbers may increase or decrease based on how effectively and consistently PrEP is taken. When an individual is taking PrEP, they must follow-up with a healthcare provider every few months.1-3

How does Truvada work?

Truvada is a combination of two NRTI medications. These medications stop the reverse transcription step of the HIV life cycle. Normally, HIV uses its reverse transcriptase enzyme to build a strand of DNA from its original RNA form (both forms of the virus’s genetic material, and how it replicates). In order to do this, it uses genetic building blocks called nucleosides that come from the host cell. These nucleosides are strung together one at a time, like beads on a string, to create the final DNA product.

NRTIs act as nucleoside mimics that stop the DNA-building process. NRTIs look like normal nucleosides, except they’re missing a special chemical group on one side. Without this group, the reverse transcriptase enzyme is unable to attach more nucleosides to the chain after them and HIV cannot continue to replicate.

When used for PrEP, the individual taking Truvada must be HIV-negative. If a previously HIV-negative individual becomes HIV-positive while taking Truvada, they must begin a new treatment regimen, as Truvada on its own is not indicated for HIV treatment. Individuals taking Truvada for PrEP must get tested for HIV every few months, as well as tested for other sexually transmitted infections.

What is PEP?

PEP (post-exposure prophylaxis) is a combination of medicines given after potential exposure to HIV has occurred. PrEP is different from PEP in that PrEP is taken before a potential exposure occurs and on a long-term basis. PEP, on the other hand, is designed to be used in emergency situations only, and after a potential exposure has occurred. PEP involves more medications at higher doses than PrEP and cannot be used on a regular basis. If you consistently have a higher risk of getting HIV, PrEP is a more beneficial, long-term option.1-4

Instances when PEP may be appropriate include:

  • After a potential workplace exposure, such as an accidental needle stick when working with an HIV-positive individual
  • After a sexual assault, especially when the HIV status of the assailant is unknown
  • After a sexual encounter with an HIV-positive individual (or potentially HIV-positive individual) in which the condom or other methods of barrier protection failed or broke
  • After sharing needles or works (things used to prepare drugs) for injection drug use with an HIV-positive individual (or a potentially HIV-positive individual)

Contact a healthcare provider or seek medical attention as soon as you think you may have been exposed to HIV. PEP needs to be started within three days (72 hours) of the exposure; the sooner the medication is started, the better it is at protecting you. PEP works the most effectively if it can be started within 24 hours of exposure, if possible.

If you think you may have been exposed to HIV at work, talk to your supervisor immediately. There are often resources available and protocols in place, especially in healthcare settings, for potential exposures to HIV and other infectious agents.4,5

The medications used in a PEP treatment regimen may vary based on an individual’s age or other medical conditions. Regardless of the exact medications used, PEP is usually taken for 28 days. The preferred treatment regimen for adults and adolescents who are in good health includes tenofovir disoproxil fumarate (300 mg) with emtricitabine (200 mg) once daily (Truvada). In addition to these medications, raltegravir (400 mg) twice daily or dolutegravir (50 mg) once daily is given as well. This regimen is also recommended for pregnant women.6

PEP can greatly reduce the chances of getting HIV after a potential exposure if it is taken exactly as prescribed; however, it is not 100 percent guaranteed to prevent the transmission of the virus.4,5

Written by: Casey Hribar | Last reviewed: September 2019
  1. Effectiveness of Prevention Strategies to Reduce the Risk of Acquiring or Transmitting HIV. Centers for Disease Control and Prevention. Published March 7, 2017. Accessed July 25, 2019.
  2. HIV/AIDS Prevention. Centers for Disease Control and Prevention. Published January 16, 2019. Accessed July 25, 2019.
  3. Pre-Exposure Prophylaxis (PrEP). Centers for Disease Control and Prevention. Published May 28, 2019. Accessed July 25, 2019.
  4. PEP. Centers for Disease Control and Prevention. Published July 23, 2018. Accessed July 25, 2019.
  5. Post-Exposure Prophylaxis (PEP). United States Department of Health and Human Services: AIDSinfo. Published May 10, 2019. Accessed July 25, 2019.
  6. Updated Guidelines for Antiretroviral Postexposure Prophylaxis After Sexual, Injection Drug Use, or Other Nonoccupational Exposure to HIV. Centers for Disease Control and Prevention. Published 2016. Accessed July 25, 2019.