While treatment for suspected HIV infection immediately after exposure is important, preventive treatment prior to exposure may be more effective as a new route in effectively preventing HIV infection in at-risk populations, according to a review published in the CMAJ (Canadian Medical Association Journal). ”While post-exposure prophylaxis has a long history of success as an approach, some new approaches such as pre-exposure prophylaxis, and early post-infection treatment (prophylaxis) have had some success in implementation.” Isaac Bogoch, MD, PhD, from Harvard Medical School, who is also on the faculty of the Department of Infectious Diseases at Massachusetts General Hospital in Boston, writes in the article with co-authors. A number of recent large randomized controlled trials have expanded knowledge of pre-exposure prophylaxis and early initiation of antiretroviral therapy. Researchers from Massachusetts General Hospital, Brigham and Women’s Hospital and Harvard Medical School in Boston and Sunnybrook Health Sciences Centre in Toronto reviewed the literature published from January 1990 to April 2012 to provide physicians with a step-by-step approach to drug prevention. HIV is transmitted primarily through unprotected sexual intercourse, contaminated needles, and mother-to-child transmission, but mother-to-child transmission is not discussed in this review. After evaluating whether an individual was exposed to HIV based on a detailed exposure history, post-exposure treatment/prophylaxis should be administered as soon as possible or within 72 hours and for 28 days. If the patient is at low risk, but not completely free of risk, the physician and patient should decide on the risk of transmission and whether to administer prophylaxis. The current approach recommends a regimen of two drugs (tenofovir and emtricitabine) in combination, plus a third drug if the patient is at high risk of exposure. ”The evidence for rapid initiation of prophylaxis and maintenance of a 4-week treatment period comes from a macaque transmission model in which later initiation of prophylaxis or shorter duration of treatment resulted in higher rates of HIV seroconversion (more anti-HIV antibodies produced in the serum),” the authors write in the paper. For high-risk groups such as men who have sex with men, intravenous drug users, and women in areas with high HIV prevalence, pre-exposure prophylaxis has been found to prevent HIV infection before they are exposed to the virus. For example, a recent trial of 900 women from areas with high HIV prevalence found that the use of topical vaginal microbicides 12 hours before and after intercourse reduced their HIV infection rates by 39%. These comprehensive programs include standardized safer sex information and condom use, testing and treatment for other sexually transmitted infections, and, in some specific cases, the promotion of male circumcision and needle exchange programs.” The authors write in the article. ”However, pre-exposure prophylaxis may not apply to high-risk exposed individuals, for whom the trend toward treating people with higher levels of CD4-positive T cells for HIV early in the course of infection appears to be an even more effective pharmacological strategy for preventing viral transmission.” The authors concluded. They note that while pre-exposure prophylaxis is very promising, some questions remain, such as which populations would benefit the most and the likely magnitude of drug resistance. Several large trials are already being implemented to determine the effectiveness of early treatment.