Question: Is there a "morning-after" pill for HIV exposure? What can be done if someone is exposed to HIV infection?

Answer: This question is arising more often in clinical practice. First, it is important to differentiate exposure in an occupational setting (e.g., a healthcare worker stuck with a needle) from a non-occupational setting (e.g., a broken condom, or shared needle while injecting). This is because the available data and guidelines are different in the two settings. While the U.S. Public Health Service (PHS) Guidelines (PDF) recommend consideration of post-exposure prophylaxis (PEP) treatment of exposed healthcare workers, the effectiveness of treatment after HIV exposure in the non-occupational setting is less clear. In the occupational setting, the recommended treatment for an exposed healthcare worker is a 2- or 3-antiretroviral-drug regimen for 1 month if the exposure is determined to be high risk.

In 1995, data from healthcare workers treated with AZT after HIV exposure showed an 81% decrease in the risk for HIV infection after needle-stick exposure to HIV-infected blood. However, AZT failed to prevent HIV infection in healthcare workers in 13 reported instances. The risk for HIV transmission per episode of unprotected receptive anal sex is estimated at 0.1% to 3% and the risk per episode of unprotected receptive vaginal sex is estimated to be even lower, at 0.1% to 0.2%. No published estimates of the risk for transmission from receptive oral sex exist, but instances of HIV transmission from oral sex have been reported.

Although animal studies indicate that antiretroviral agents are most effective within 1 to 2 hours of exposure and probably not effective when started later than 24 to 36 hours after exposure, the interval during which therapy can be beneficial for humans is unknown. Researchers in San Francisco have reported on over 100 people who received PEP for non-occupational HIV exposure and there were no cases of HIV infection in that group. However, given the relatively low rate of HIV transmission per unprotected sexual contact, it is not known how many infections there would have been had PEP not been used.

The above data and recommendations were published in September 1998, by the Centers for Disease Control (CDC) in a report titled, Management of Possible Sexual, Injecting-Drug-Use, or Other Non-Occupational Exposure to HIV, Including Considerations Related to Antiretroviral Therapy. The conclusion of that report was that because of the lack of efficacy data for the use of antiretroviral agents to reduce HIV transmission after a possible non-occupational exposure, PHS is unable to recommend for or against this therapeutic approach. Additionally, the report recommended that if such therapy is attempted, healthcare providers must inform patients of the lack of data, address their patients' underlying risk-reduction needs (when applicable), and restrict the use of this therapy to high-risk exposures (e.g., unprotected receptive anal or vaginal intercourse with a known HIV-positive person). Also, the report recommended that more research is needed in this area. Following this report, the CDC initiated a surveillance system to collect information about persons who seek medical care after possible sexual, injecting-drug use, or other non-occupational HIV exposures.

In clinical practice, the factors considered in deciding whether to recommend PEP include the nature of the exposure; the HIV status and treatment history of the contact, including viral load, if known; and the time of the exposure. The animal data shows that, after more than 24 hours after exposure, the effectiveness of PEP decreases significantly, and there is probably no benefit if PEP is begun more than 72 hours after exposure. Even if PEP is recommended, there is no "morning-after" pill. The treatment is for 1 month, with two or three drugs that often have significant side effects.

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Dr. Jeff Schouten is a former general surgeon who has been living with HIV for over 15 years. He is chair of STEP's Publications Advisory Committee and contributes regularly to the STEP Perspective_. He has also earned a law degree from the University of Washington, so HIV-related legal questions, as well as medical, will be considered._