What Is Post-exposure Prophylaxis?

What is post-exposure prophylaxis?

With PEP, an HIV-negative person who may have been exposed to HIV takes anti-HIV drugs prescribed by a doctor to prevent infection. These are the same drugs that people living with HIV take. PEP involves taking two or three of these drugs for a period of one month. To effectively reduce a person’s risk of becoming HIV-positive, PEP must be taken within 72 hours of possible exposure to HIV but ideally as early as possible.  

In the world of PEP, exposure to HIV is often divided into two categories: occupational exposure and non-occupational exposure. “Occupational” exposure refers to exposure to HIV at work, in a healthcare setting. For example, a healthcare provider could be exposed to HIV through a needlestick injury at work. “Non-occupational” exposure refers to exposure to HIV through sex or drug use, for example, when a person shares a needle or has sex without a condom.

What is the rationale for PEP?

In the first one to three days following exposure to HIV, there is a ‘window of opportunity’ when taking PEP might prevent an HIV infection from occurring.1 During this ‘window of opportunity,’ the virus is busy infecting cells at the site of exposure (such as in the anus, penis or vagina). Once the virus is inside a cell, it starts replicating to produce more HIV (also known as virions). After a few days, these new HIV virions start to spread throughout the body; once this happens, infection is permanent. The theory is that if PEP is given to a person early enough, it can stop the virus from replicating at the initial site of exposure, preventing virions from spreading throughout the body – stopping the infection from becoming permanent. The cells that initially became infected would eventually die out and the virus would not be able to replicate.   

What is the evidence on PEP?

There is some evidence that suggests that providing PEP after a potential exposure to HIV can help reduce a person’s risk of HIV infection. However, we also know that PEP is not 100% effective, meaning that it will not prevent all HIV infections.

Learn more about the evidence on PEP

What does someone need to know to access PEP?

People at risk need to know that PEP exists. If people are unaware of PEP, they won’t know that PEP is an option in the event of a high-risk behaviour that could result in being exposed to HIV. Very little research has been done to determine how many people are aware of PEP; however, based on the research that has been done, it seems that only a small proportion of gay and heterosexual men and women, even in cities with well-established PEP programs, are aware of PEP.9,10,11,12

People at risk need to know that time is of the essence. The later someone starts PEP, the less likely it is to prevent HIV infection. The best time to start PEP is immediately after exposure. However, PEP has some ability to prevent HIV infection up to 72 hours after infection.

People at risk need to know where to go. PEP must be prescribed by a doctor. Since time is of the essence, people need to be able to access services that are always open, such as emergency rooms. As a service provider, it may be important for you to know if there is a physician or healthcare facility in your area willing to prescribe PEP. If there isn’t, perhaps your organization can inform local clinicians of PEP and push for access to PEP for your clients.

Anyone accessing PEP will be tested for HIV. PEP is used to prevent HIV, not to treat it. People who go to a healthcare facility for PEP will be tested for HIV. They will still be prescribed PEP while the test results are pending; however, if the result is positive, PEP may either be discontinued or the anti-HIV drugs may be changed to HAART (highly active antiretroviral therapy) to treat the person’s HIV infection.

PEP can be costly and it may have to be paid for out of pocket. The cost of a full course of PEP is approximately $1100 to $1500. PEP may be covered by some private insurance plans and some public health insurance plans, depending on the province and the nature of the exposure. However, many at-risk individuals may not have access to any drug coverage and may not be able to afford it. There may be a need for advocacy in your area or province to fight for universal access to PEP.  

People on PEP may experience side effects. Depending on the anti-HIV drugs prescribed, people may experience side effects from PEP, such as fatigue, nausea or diarrhea. This can cause people to stop taking their PEP drugs as prescribed, which can decrease the ability of the medications to prevent HIV infection and increase the likelihood of being infected with a drug-resistant strain of HIV.

People on PEP have to be monitored by a doctor. Testing for toxicity will be required to make sure the drugs are not causing harm to the body. The type of tests may differ depending on the anti-HIV drugs that are prescribed but would likely include liver and kidney tests.

PEP can fail to prevent HIV infection if someone doesn’t take the anti-HIV drugs as prescribed. Taking the anti-HIV drugs exactly as prescribed (also known as adherence) is central to the success of PEP. If someone doesn’t take their PEP as prescribed, then HIV infection could occur. There are two issues with adherence:

Some people might start PEP but stop using it early (before the four weeks are over). In research studies 24% to 78% of people who started PEP stopped taking it early.13
Some people may not take their PEP exactly as prescribed. For example, some people may occasionally forget doses, or take only every second dose.  
Drug resistance can develop if a person doesn’t take the anti-HIV drugs as prescribed. If a person becomes HIV-positive due to non-adherence, they may develop drug resistance. When someone does not take PEP as prescribed, the amount of anti-HIV drugs in the blood can be too low to suppress the HIV, which can allow the virus to evolve and develop resistance. It is important to understand that infection with a drug-resistant strain of HIV limits a person’s future treatment options. If a person with a drug-resistant strain of HIV subsequently infects someone else with HIV, drug resistance spreads within the community.

Community agencies can provide adherence support for people on PEP by providing ongoing consultation and encouragement to help people take PEP exactly as prescribed and to complete their treatment.

PEP may fail to prevent HIV infection due to drug resistance. If a person is exposed to a drug-resistant strain of HIV and the person is prescribed the drug they are resistant to, as part of their PEP regime, then PEP may fail to prevent HIV infection. Unfortunately, there is no way to know within the first one to three days if someone has been exposed to drug-resistant HIV.