Post-exposure prophylaxis
Post-exposure prophylaxis, also known as post-exposure prevention, is any preventive medical treatment started after exposure to a pathogen in order to prevent the infection from occurring.
Rabies
PEP is commonly and very effectively used to prevent the onset of rabies after a bite by a suspected-rabid animal, since diagnostic tools are not available to detect rabies infection prior to the onset of the nearly always-fatal disease. The treatment consists of a series of injections of rabies vaccine and immunoglobulin. Rabies vaccine is given to both humans and animals who have been potentially exposed to rabies.Tetanus
toxoid can be given in case of a suspected exposure to tetanus. In such cases, it can be given with or without tetanus immunoglobulin. It can be given as intravenous therapy or by intramuscular injection.The guidelines for such events in the United States for non-pregnant people 11 years and older are as follows:
| Vaccination status | Clean, minor wounds | All other wounds |
| Unknown or fewer than three doses of tetanus toxoid containing vaccine | Tdap and recommend catch-up vaccination | Tdap and recommend catch-up vaccination Tetanus immunoglobulin |
| Three or more doses of tetanus toxoid containing vaccine AND less than 5 years since last dose | No indication | No indication |
| Three or more doses of tetanus toxoid containing vaccine AND 5–10 years since last dose | No indication | Tdap preferred or Td |
| Three or more doses of tetanus toxoid containing vaccine AND more than 10 years since last dose | Tdap preferred or Td | Tdap preferred or Td |
HIV
History
was approved as a treatment for AIDS in 1987. Healthcare workers would occasionally 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 questions arose of whether to give HIV treatment after known exposure or high risk of exposure. Early data from pre-clinical studies established the efficacy of AZT in preventing transmission of HIV infection. AZT was also seen to reduce maternal-infant transmission of HIV in a randomized controlled trial, suggesting AZT's post-exposure prophylaxis use. Subsequent data show combination antiretroviral therapy is significantly superior than AZT in reducing perinatal transmission rates. In addition, AZT is generally no longer recommended due to poor tolerance resulting in high rates of patient noncompliance.
Non-occupational exposures include cases 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. In 2005, the US DHHS released the first recommendations for non-occupational PEP use to lower risk of HIV infection after exposures. The recommendations were replaced with an updated guideline in 2016.
Occupational exposures include needlestick injury of health care professionals from an HIV-infected source. In 2012, the US DHHS included guidelines on occupational PEP use for individuals with HIV exposures occurring in health care settings.
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 by taking medication before a potential exposure to HIV occurred.
A report from early 2013 revealed that a female baby born with the HIV virus displayed no sign of the virus two years after high doses of three antiretroviral drugs were administered within 30 hours of her birth. The findings of the case were presented at the 2013 Conference on Retroviruses and Opportunistic Infections in Atlanta, U.S. and the baby is from Mississippi, U.S. The baby—known as the "Mississippi baby"—was considered to be the first child to be "functionally cured" of HIV. However, HIV re-emerged in the child as of July 2014.
Risk evaluation
Initiation of post-exposure prophylaxis with the use of antiretroviral drugs is dependent on a number of risk factors, though treatment is usually started after one high-risk event. In order to determine whether post-exposure prophylaxis is indicated, an evaluation visit will be conducted to consider risk factors associated with developing HIV. Assessments at this visit will include whether the at-risk person or the potential source-person are HIV positive, details around the potential HIV exposure event, including timing and circumstances, whether other high-risk events have occurred in the past, testing for sexually transmitted diseases, testing for hepatitis B and C, and pregnancy tests for women of childbearing potential.Risk factors for developing HIV includes exposure of mucous membranes of an HIV-negative person to bodily fluids of a person known to be HIV positive. For example, having unprotected sex with HIV positive partner is considered risky, but sharing sex toys, spitting and biting considered to be negligible risks for initiating post-exposure prophylaxis. The highest non-sexual risk is blood transfusion and the highest sexual contact risk is receptive anal intercourse. The timing of exposure does not affect the risk of developing HIV, but it does alter whether post-exposure prophylaxis will be recommended. Exposures that occurred 72 hours or less to beginning treatment are eligible for post-exposure prophylaxis. If the exposure occurred over 73 hours prior to treatment initiation, post-exposure prophylaxis is not indicated.
Testing
Initial HIV testing: Before initiating PEP after potential HIV exposure, persons should be tested for HIV1 and HIV2 antigens and antibodies in the blood using a rapid diagnostic test. PEP should only be started if rapid diagnostic test reveals no HIV infection present or if tests results are not available. However, if HIV infection is already present then PEP should not be started. HIV test should be repeated four to six weeks and three months after exposure.People may experience signs and symptoms of acute HIV infection, including fever, fatigue, myalgia, and skin rash, while taking PEP. CDC recommends seeking medical attention for evaluation if these signs and symptoms occur during or after the month of PEP. If follow-up laboratory antibody tests reveal HIV infection, HIV treatment specialists should be sought out and PEP should not be discontinued until person is evaluated and treatment plan is established.
STI and HBV testing: People with potential exposure to HIV are also at risk of acquiring STI and HBV. Centers for Disease Control and Prevention recommends STI-specific nucleic acid amplification testing for gonorrhea and chlamydia and blood tests for syphilis. PEP is also active against HBV infections so discontinuation of medication can cause the reactivation of HBV, though rare. Health care providers must monitor HBV status closely.
Follow up testing: Serum creatinine and estimated creatinine clearance should be measured at baseline to determine the most appropriate PEP antiretroviral regimen. While on PEP, liver function, renal function, and hematologic parameters should be monitored.
Treatment
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. 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, the level of exposure, and/or the duration of treatment. In addition, since the time and level of non-occupational exposures are self-reported, there is no absolute data on the administration timeframe to which PEP would be efficacious. The standard antibody window period begins after the last day of PEP treatment. People who received PEP are typically advised 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. People initiating nPEP treatment typically receive a 28-day starter pack, as opposed to a 3-7 day starter pack, to facilitate strong medication adherence. They should also be counseled on the unpleasant side effects including malaise, fatigue, diarrhea, headache, nausea and vomiting.
People at high risk for re-exposure due to unprotected intercourse or other behavioral factors should be given PrEP, which would begin immediately after the completion of the nPEP treatment course. Inversely, if a medically-adherent patient is already on PrEP upon non-occupational exposure, nPEP treatment is not necessary.