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Pre-exposure Prophylaxis (PrEP) of HIV |
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Pre-exposure prophylaxis (PrEP) of HIV refers to an HIV-prevention strategy in which HIV-negative people take a drug on a regular basis to reduce their risk of acquiring HIV. PrEP for HIV is based on the concept that drugs can be used by healthy people to prevent certain infections. For example, travelers use prophylactic drugs to avoid malaria. Just as a prophylactic antimalarial drug circulates in a person's bloodstream before any encounter with a mosquito, a PrEP drug would be in a person's body before any exposure to HIV. In theory, the PrEP drug would prevent HIV from reproducing itself inside the body, and so prevent the development of disease. Scientists are now conducting clinical trials to determine whether a potential PrEP drug could reduce an adult's chance of becoming infected with HIV. This description focuses on the use of pills (oral PrEP) rather than gels (topical microbicides) that are applied to the vagina or rectum. The Need for a PrEP Drug Nearly 7,000 people around the world become infected with HIV every day.1 Unfortunately, an effective HIV vaccine is still years away, and current prevention options are not always practical for many people. For example, one prevention approach -- known as "behavior change" -- requires consistent changes in sexual behavior and the use of a condom by the male partner. Because women often have difficulties negotiating the use of condoms, a new method that women can use is urgently needed. The development of an effective PrEP drug would provide an important new way to reduce HIV infection rates among women and men. Antiretroviral Drugs Although we do not have a PrEP drug for adults, scientists have found drugs that reduce the mother-to-child transmission of HIV -- important evidence that PrEP may prove effective when it is used by uninfected people. For example, a single dose of an antiretroviral drug (ARV) called nevirapine, given to an HIV-positive mother during labor, and another dose given to the baby after birth, reduces the mother-to-child transmission of HIV by nearly 50 percent.2 Similarly, if a person is exposed to HIV through a needle-stick injury, there is evidence that a course of ARVs taken after the exposure may reduce the person's chance of developing HIV/AIDS. This treatment is called post-exposure prophylaxis. Most ARVs are currently used to treat people who are HIV positive, but scientists believe that the prophylactic use of ARVs may also help to reduce the chance that an HIV-negative adult will become infected with HIV. Pre-exposure use of ARVs may also have an impact on the course of an infection if an HIV-negative person does become infected. The ARV drug tenofovir (TDF) and a combination of TDF and emtricitabine (FTC) are currently being tested in clinical trials for use as PrEP. Read more The Safety and Side Effects of Antiretroviral Drugs The ARVs that are used in current PrEP trials have been shown to be safe when taken by HIV-positive people for the treatment of HIV/AIDS. These ARVs are licensed for use as treatments by government agencies around the world, including the United States Food and Drug Administration. One of the first PrEP trials, a study conducted among HIV-negative women in West Africa, found that tenofovir was just as safe as a placebo.3 In current PrEP trials, scientists are carefully monitoring the safety of PrEP, and they will stop any trial if the drug appears to harm the participants. The most common side effects reported by HIV-positive people who take ARVs for treatment are nausea, diarrhea, vomiting, and intestinal gas. Some evidence exists that tenofovir may affect liver or kidney function in people with HIV. It may also reduce bone density in some patients. Scientists do not know whether the side effects in HIV-negative people who take a PrEP drug in a clinical trial will be the same as those in HIV-positive people who take the drug as a treatment. PrEP Clinical Trials PrEP clinical trials are now underway by Family Health International and other organizations to determine whether an ARV, or a combination of ARV drugs, can reduce the chance that an HIV-negative person will become infected with HIV. Trials are currently planned or underway in Africa, Asia, Latin America, and North America. These studies are looking at the safety and effectiveness of PrEP. The first results from the current PrEP effectiveness trials may become available as early as 2009. Readers can find an up-to-date list of the trials here. The Use of PrEP A new PrEP drug might not be 100-percent effective. But even if PrEP only reduces the risk of acquiring HIV by 50 or 60 percent, it will be an important contribution to the fight against HIV/AIDS. Despite the potential value of an effective PrEP drug, the possibility that it may provide only "partial protection" raises some concerns about its use by the public. If people believe that they cannot become infected with HIV because they take a PrEP drug, they may be less careful about protecting themselves in other ways. For example, some individuals may decide that they do not need to use condoms or they may begin to engage in risky sex practices. Such disinhibition may actually increase their rate of infection because no PrEP regimen will offer complete protection. Because of this possibility, PrEP needs to be accompanied by counseling that explains the notion of partial protection and the need for condoms and other risk-reduction strategies. Some scientists are also concerned about drug "resistance." If a person continues to take a PrEP drug after they became infected with HIV, he or she could develop a form of the virus that is resistant to the ARV. Resistance happens when HIV adapts to an ARV, so the drug is less effective as a treatment for an HIV infection. This is more likely to happen when an HIV-positive person is taking only one ARV or when someone does not take the ARV as prescribed. In such instances, another ARV could be used in combination with the original PrEP drug as a treatment. References
Other resources The AIDS Vaccine Advocacy Coalition (AVAC) and the UCLA Program in Global Health maintain a comprehensive Web site on PrEP. Anticipating the Results of PrEP Trials: A Powerful New HIV Prevention Tool May Be on the Horizon. Are We Prepared? (August 2008, PDF, 524 KB) |
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