From the Guidelines
Post-exposure prophylaxis (PEP) started at 7 weeks after exposure is not recommended as it would be ineffective. The most recent and highest quality study, published in 2016 in JAMA 1, recommends that PEP should be initiated as soon as possible, but only within 72 hours of exposure. This is because the efficacy of PEP is likely highest when started promptly, with an estimated efficacy rate of 81% for zidovudine monoprophylaxis 1.
After 7 weeks, if HIV transmission occurred during the exposure, the virus would have already established infection in the body, making PEP futile. Instead, the person should immediately get tested for HIV using a 4th generation antigen/antibody test, which can detect HIV infection by this time. If positive, the person should be linked to HIV care for antiretroviral therapy. If negative, they should consider pre-exposure prophylaxis (PrEP) if they have ongoing risk.
Some older studies, such as the 1996 study published in Morbidity and Mortality Weekly Report 1, suggest that initiating therapy after a longer interval may be considered for the highest risk exposures, but this is not supported by the most recent evidence. The 2016 study 1 recommends that PEP should be continued for 28 days, and HIV serostatus should be reassessed 4 weeks to 6 weeks, 3 months, and 6 months after exposure.
Key points to consider:
- PEP must be initiated within 72 hours of potential HIV exposure to have a chance of preventing infection
- After 7 weeks, PEP is no longer effective in preventing HIV infection
- The person should get tested for HIV using a 4th generation antigen/antibody test
- If positive, the person should be linked to HIV care for antiretroviral therapy
- If negative, they should consider pre-exposure prophylaxis (PrEP) if they have ongoing risk
From the Research
Post-Exposure Prophylaxis (PEP) Initiation Timing
- The recommended timing for initiating PEP is as soon as possible after exposure, with initiation discouraged after 72 hours 2, 3.
- Starting PEP within 1-4 hours from the exposure is strongly recommended 4.
- There is no evidence to support the initiation of PEP at 7 weeks post-exposure, as all studies emphasize the importance of starting PEP as soon as possible after exposure.
PEP Recommendations
- PEP should be initiated with a triple combination of antiretrovirals approved for the treatment of HIV-infected patients 2, 3.
- A two-class regimen is preferred 2.
- The source patient's treatment history should be sought 2.
- Counselling, psychological support, HIV testing, and clinical evaluation should be performed at baseline, at 6-8 weeks, and at least 6 months post-exposure 2.
Monitoring and Follow-up
- Additional clinical and laboratory monitoring at one and two weeks should be considered to assess adherence and potential toxicity 2, 3.
- HIV testing should be performed at baseline, 4,12, and 24 weeks 3.
- Routine HIV resistance tests in the source patient and direct virus assays in the exposed individual are not recommended 2, 3.