Post-exposure prophylaxis (PEP) is any prophylactic treatment started immediately after exposure to a pathogen (such as a disease-causing virus), in order to prevent infection by the pathogen and the development of disease.
PEP is commonly and very effectively used to prevent the outbreak of rabies after a bite by a rabid animal.
Tetanus post-exposure consists of 2 to 3 injections of tetanus vaccine and tetanus immunoglobulin.
AZT was approved as a treatment for AIDS in 1987. As AIDS patients started seeking treatment in medical centers, it sometimes happened that a healthcare worker would be exposed to HIV during work. Some people thought to try giving health care workers AZT to prevent seroconversion. This practice dramatically decreased the incidence of seroconversion among health workers when done under certain conditions.
Later the question arose of whether to give HIV treatment to people who had non-occupational exposure, for example, when a condom breaks while a person with HIV has unprotected sex with an HIV-negative person in a single incidence, or in the case of unprotected sex with an anonymous partner, or in the case of a non-habitual incident of sharing a syringe for injection drug use. Evidence suggests that PEP also reduces the risk of HIV infection in these cases.
Since taking HIV-attacking medications shortly after exposure was proven to reduce the risk of contracting HIV, this led to research into pre-exposure prophylaxis, which would mean taking medication before any exposure to HIV in anticipation of being in a situation which was likely to expose one to HIV infection.
In the case of HIV exposure, post-exposure prophylaxis is a course of antiretroviral drugs which reduces the risk of seroconversion after events with high risk of exposure to HIV (e.g., unprotected anal or vaginal sex, needlestick injuries, or sharing needles). The CDC recommends PEP for any HIV negative person who has recently been exposed to HIV for any reason.
To be most effective, treatment should begin within an hour of exposure. After 72 hours post-exposure PEP is much less effective, and may not be effective at all. Prophylactic treatment for HIV typically lasts four weeks.
While there is compelling data to suggest that PEP after HIV exposure is effective, there have been cases where it has failed. Failure has often been attributed to the delay in receiving treatment (greater than 72 hours post-exposure), the level of exposure, duration of treatment (lack of adherence to the 28 day regimen), or all three. However, given that — for non-occupational exposures — the time and level of exposure are based on patient-supplied information, absolute data is unavailable. PEP can also slow down the development of antibodies while the medications are still being taken. This can result in false negatives on an antibody test if the proper waiting period is not observed after completion of medications. The standard antibody window period begins after the last day of PEP treatment. Doctors will advise patients who received PEP to get an antibody test at 6 months post-exposure as well as the standard 3 month test.
The antiretroviral regimen used in PEP is the same as the standard highly active antiretroviral therapy used to treat AIDS. It requires close compliance and can have unpleasant side effects including malaise, fatigue, diarrhea, headache, nausea and vomiting.
Hepatitis A 
Hepatitis B 
If the person exposed is an HBsAg positive source (a known responder to HBV vaccine) then if exposed to hepatitis B a booster dose should be given. If they are in the process of being vaccinated or are a non-responder they need to have hepatitis B immune globulin (HBIG) and the vaccine. For known non-responders HBIG + vaccine should be given whilst those in the process of being vaccinated should have an accelerated course of HBV vaccine.
Hepatitis C 
Persons exposed to Hepatitis C should get monthly PCR - if seroconversion then interferon +/- ribavirin.
See also 
- Pre-exposure prophylaxis (PrEP)
- "WHO". Retrieved 2008-03-05. Text " Guide for post-exposure prophylaxis " ignored (help)
- Cardo, D. M.; Culver, D. H.; Ciesielski, C. A.; Srivastava, P. U.; Marcus, R.; Abiteboul, D.; Heptonstall, J.; Ippolito, G. et al. (1997). "A Case–Control Study of HIV Seroconversion in Health Care Workers after Percutaneous Exposure". New England Journal of Medicine 337 (21): 1485–1490. doi:10.1056/NEJM199711203372101. PMID 9366579.
- Katz, M. H.; Gerberding, J. L. (1997). "Postexposure Treatment of People Exposed to the Human Immunodeficiency Virus through Sexual Contact or Injection-Drug Use". New England Journal of Medicine 336 (15): 1097–1100. doi:10.1056/NEJM199704103361512. PMID 9091810.
- Smith, Dawn K.; Grohskopf, Lisa A.; Black, Roberta J.; Auerbach, Judith D.; Veronese, Fulvia; Struble, Kimberly A. (21 January 2005). "Antiretroviral Postexposure Prophylaxis After Sexual, Injection-Drug Use, or Other Nonoccupational Exposure to HIV in the United States". cdc.gov. Centers for Disease Control. Retrieved 7 July 2011.
- Diprose, P; Deakin, C.D.; Smedley, J (2000). "Ignorance of post-exposure prophylaxis guidelines following HIV needlestick injury may increase the risk of seroconversion". British Journal of Anaesthesia 84 (6): 767–770. Retrieved 7 July 2009.
- "HIV/AIDS Bureau - HIV Care Pocket Guide 2006 - Occupational HIV Postexposure Prophylaxis (PEP)". Retrieved 2008-03-05.
CDC on nonoccupational HIV postexposure prophylaxis, an article which summarizes more than 100 related research projects