Antiretroviral Drugs—PEP, PrEP and Treatment as Prevention

Antiretroviral Drugs—PEP, PrEP and Treatment as Prevention

Researchers are exploring three ways to use HIV drugs to prevent HIV transmission:
Post-exposure prophylaxis (PEP): PEP involves taking a short course of ARV drugs, usually for a month, after a high-risk exposure. Though experts believe that PEP works, based on large amounts of data in health care workers who were exposed to infected blood, it is not possible to ethically test this in humans for sexual exposure. To be most effective, PEP should be started immediately after possible exposure, waiting no more than 72 hours. If you suspect a high-risk exposure to HIV—semen leaking out of a condom during intercourse with an HIV-positive insertive partner; receptive anal sex without a condom with a partner who is either HIV positive or whose status you do not know or you have shared drug-injection works with someone who is either HIV positive or whose status you do not know—contact your health care provider or local hospital emergency room as soon as possible.


Pre-exposure prophylaxis (PrEP): PrEP involves having an uninfected person take ARV drugs—usually Viread (tenofovir) or Truvada (tenofovir plus emtricitabine)—before, during and after possible high-risk exposures to reduce the risk of becoming infected. The earliest PrEP studies call for taking either Viread or Truvada every day, even during periods of minimal or low-risk sexual activity. Future studies may explore intermittent dosing strategies (e.g., using PrEP only during periods of high-risk sexual or drug-using activity). A recent study found that taking the oral HIV drug Truvada (tenofovir plus emtricitabine), when combined with condoms and counseling, was able to prevent infection by 44 percent in men who have sex with men (MSM) and transgender women who have sex with men. In those who reported taking at least 90 percent of their doses correctly, Truvada cut infections by 73 percent. The CDC, however, is cautioning people not to begin using PrEP on their own.

There are a number of reasons for this, including the fact that we don't yet know how frequently a person needs to get tested while on PrEP. If a person does become infected, and continues to use Truvada before they next get tested, they could become resistant to one or both of the drugs contained in the combination pill. Second, the study was only conducted in MSM and we don't yet know how well it will work to prevent transmission from vaginal sex or from injection drug use. There are four other PrEP studies currently in progress, and it will be important to see how well PrEP works in other populations and settings before firm recommendations can be issued. The CDC is currently working on interim guidelines for providers.
Treatment-as-prevention: In 2009, a Swiss medical committee issued a statement concluding that if an HIV-positive person's viral load is undetectable for at least six months while using ARV therapy, the risk of transmitting this virus to an HIV-negative partner is essentially nil (both partners also need to be free of other sexually transmitted diseases). This statement has been controversial, as the studies referenced in the statement primarily involved heterosexual couples in long-term monogamous relationships and do not account for the variables in real-world situations (e.g., HIV-positive individuals with multiple partners, individuals engaging in unprotected anal sex, people on ARV treatment with drug resistance and detectable viral loads, etc.). Though the risk may not necessarily be zero, experts agree that an HIV-positive person with an undetectable viral load is significantly less likely to transmit his or her virus to an HIV-negative partner. This understanding has prompted additional research to explore not only the personal benefits of treatment—AIDS-free survival for the person infected with HIV—but also the public health implications of getting all HIV-positive people, especially those who are unaware of their status, in to care and on treatment to reduce the ongoing spread of HIV. Studies are getting under way now to help determine whether very early treatment of people with HIV—started as soon as possible after testing positive—might help reduce the overall number of new infections within a community. In the interim, public health officials in some cities have already begun recommending that all people with HIV begin taking antiretroviral therapy regardless of their current CD4 count.