Typically, post-exposure prophylaxis (PEP) refers to medications given in the health care setting after exposure to potentially harmful material through a needle stick or splash. PEP is given to try to prevent infection with HIV. Sometimes PEP can include hepatitis vaccines as well. The Centers for Disease Control and Prevention (CDC) has issued fairly specific guidelines to the use of PEP for the prevention of HIV in health care workers (HCWs). Various regimens are used depending on the severity of exposure and the HIV status of the source. But what about PEP for sexual exposure?
The CDC does not currently have any guidelines for this. But the concept is very real. The condom breaks, you swallow, you have your period, you develop a sore, he said he was negative, you meant to pull out, you meant to remember that canker sore. Is there a role for PEP after a sexual adventure -- or misadventure?
We know from data on PEP in HCWs and also from studies of the role of AZT in reducing vertical transmission of HIV in pregnant women that PEP can work. There are no studies reporting the effectiveness of PEP for sexual exposure. Theoretically it should work. There are, however, a variety of factors which would determine whether PEP after sexual exposure is reasonable.
First of all, what is the sexual exposure? Estimates of the per-episode risk of HIV infection are variable. Receptive anal intercourse is the riskiest with an estimated .008 to .032 encounters leading to infection. Receptive vaginal intercourse carries a 0.0005 to 0.0015 risk and insertive vaginal sex is 0.0003 to 0.0009. That is, if there are 1000 HIV-negative men having unprotected receptive anal sex with an HIV-positive partner, (BIG party), it's estimated that as few as 8, as many as 32 will acquire HIV infection from that exposure. Oral sex and insertive anal sex have not been quantified but are not without their risk. These numbers can be terribly misleading. As too many people can attest: all it takes is once.
There are host factors -- the host being the one exposed to the blood or body fluid. Host factors include whether that person is already HIV infected but doesn't know it. Does the host practice safer sex as an exception or as a rule? Is re-exposure likely? Does the host want to take a four-week course of medication? How recently did the sexual exposure take place? As with PEP in the workplace, the sooner the PEP can be started (within hours, preferably), the more effective it is predicted to be.
There are source factors -- the source being the person(s) who might be exposing their blood or body fluid to the host. Is the source known to be HIV positive or is there a history of practices that would put his or her HIV status in question? If the source is infected are they taking medication for their HIV? Is it working? Was the source a rapist?
PEP is Not a Substitute for Safer Sex
PEP after sexual exposure is not appropriate for people who are unwilling or unable to practice safer sex. It is not a substitute for safer sex. It is not indicated in situations where the exposure risk is low or where the source's status and risk factors are unknown.
There is no guarantee that PEP after sexual exposure will work.
PEP is most appropriate for people who are not HIV positive, who have been exposed through receptive anal or vaginal sex in an isolated incident to a partner who is HIV infected. The host should be someone who practices safer sex and is willing to continue doing so.
Treatment recommendations following occupational exposure are in most cases applicable to sexual exposures. Treatment usually consists of two drugs given for four weeks. If the source is known to have a high viral load, a third drug can be added. Specific drugs and doses should be discussed at length because none of the anti-retroviral drugs are benign.
In the PEP Registry for HCWs, 76 percent of those who followed up for four to six weeks reported symptoms or problems. In this registry, half of those begun on PEP did not complete the treatment course. In those who did not complete the course half were discontinued because the source tested negative. The other half discontinued because of intolerance to the regimen.
Recently the drug Viramune (nevirapine) has come under scrutiny as the cause of near-fatal liver damage in two HCWs taking it for PEP.
The use of PEP must be carefully considered when accidents happen or when mistakes occur. While PEP in the health care setting has been beneficial, it has not been absolutely effective.
There is no guarantee that PEP after sexual exposure will work. Nor will it replace consistent safer sex practices on the part of everyone.