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Post-exposure prophylaxis

Post-exposure prophylaxis

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Post-exposure prophylaxis (PEP) is any prophylactic treatment started immediately after exposure to a pathogen (such as a disease-causing virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

), 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
Rabies is a viral disease that causes acute encephalitis in warm-blooded animals. It is zoonotic , most commonly by a bite from an infected animal. For a human, rabies is almost invariably fatal if post-exposure prophylaxis is not administered prior to the onset of severe symptoms...

 after a bite by a rabid animal.

The treatment consists of repeated injections of rabies vaccine
Rabies vaccine
Rabies vaccine is a vaccine used to control rabies. Rabies can be prevented by vaccination, both in humans and other animals.-In animals:Currently, pre-exposure immunization has been used on domesticated and normal non-human populations...

 and immunoglobulin.


Zidovudine or azidothymidine is a nucleoside analog reverse-transcriptase inhibitor , a type of antiretroviral drug used for the treatment of HIV/AIDS. It is an analog of thymidine....

 was approved as a treatment for AIDS in 1987. As AIDS patients started seeking treatment in medical centers, it sometimes rarely happened that somehow a healthcare worker would be exposed to HIV in the course of their occupation. Since healthcare workers were in a clinical setting anyway, AZT was at hand, and some people thought to try giving them 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 two serodiscordant
Serodiscordant is a term used to describe a couple in which one partner is HIV positive and the other is HIV negative. Serodiscordant relationships are also referred to as "magnetic". The term seroconcordant is its antonym, used to describe a couple in which both partners are of the same HIV...

 people have unprotected sex in a single incidence such as when a condom breaks, 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
Drug injection
In substance dependence and recreational drug use, drug injection is a method of introducing a drug into the body with a hollow needle and a syringe which is pierced through the skin into the body...

. 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
Pre-exposure prophylaxis
Pre-exposure prophylaxis is any medical or public health procedure used before exposure to the disease causing agent, its purpose is to prevent, rather than treat or cure a disease. An example would be if a doctor gave a medication used to treat a disease to a healthy person who is not thought to...

, 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
Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...

 infection, post-exposure prophylaxis is a course of antiretroviral drugs which reduces the risk of seroconversion
Seroconversion is the development of detectable specific antibodies to microorganisms in the blood serum as a result of infection or immunization. Serology is used to determine antibody positivity...

 after events with high risk of exposure to HIV (e.g., unprotected anal
Anal sex
Anal sex is the sex act in which the penis is inserted into the anus of a sexual partner. The term can also include other sexual acts involving the anus, including pegging, anilingus , fingering, and object insertion.Common misconception describes anal sex as practiced almost exclusively by gay men...

 or vaginal sex, needlestick injuries, or sharing needles
Needle sharing
Needle sharing is the practice of intravenous drug-users by which a syringe is shared by multiple individuals to administer intravenous drugs, and is a primary vector for diseases which can be transmitted through blood ....

). 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 infection. 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, the level of exposure (i.e., the viral load received), or both. However, for non-occupational exposures, the time and level of exposure are based on patient-supplied information; absolute data is therefore unavailable. PEP can also slow down the development of antibodies, potentially causing false negatives on a later HIV test. Doctors will advise patients who received PEP to get a 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
Malaise is a feeling of general discomfort or uneasiness, of being "out of sorts", often the first indication of an infection or other disease. Malaise is often defined in medicinal research as a "general feeling of being unwell"...

, fatigue
Fatigue (physical)
Fatigue is a state of awareness describing a range of afflictions, usually associated with physical and/or mental weakness, though varying from a general state of lethargy to a specific work-induced burning sensation within one's muscles...

, diarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...

, headache
A headache or cephalalgia is pain anywhere in the region of the head or neck. It can be a symptom of a number of different conditions of the head and neck. The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the...

, nausea
Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...

 and vomiting
Vomiting is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose...


Hepatitis A

Human Normal Immunoglobulin (HNIG) or hepatitis A vaccine may be used as PEP depending on the clinical situation.

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.

External links

CDC on nonoccupational HIV postexposure prophylaxis, an article which summarizes more than 100 related research projects