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Reducing the Transmission of HIV

Daily Dose of HIV Drug Reduces Risk of Infection

In a major advance for HIV prevention, NIAID-supported researchers found that a daily dose of an oral antiretroviral drug, currently approved to treat HIV infection, reduced the risk of HIV acquisition among men who have sex with men (MSM) by 43.8 percent. This reduction was even greater among those who most closely adhered to the drug regimen (72.8 percent).

The study, known as iPrEx, involved 2,499 adult MSM and transgendered women who have sex with men at 11 sites in Brazil, Ecuador, Peru, South Africa, Thailand, and the United States. The participants were randomly assigned to receive either a daily antiretroviral pill containing combination emtricitabine and tenofovir, known by the brand name Truvada, or a placebo. In addition, all subjects received HIV testing, risk-reduction counseling, condoms, and treatment of other sexually transmitted diseases.

Of the 100 cases of HIV infection that occurred among iPrEx study participants, 36 were among those who received Truvada compared with 64 among the placebo group. The drug appeared to be safe and well-tolerated with mild and infrequent side effects reported by a small number of participants. Additionally, very little drug resistance occurred, with no instances of tenofovir resistance and only three cases of emtricitabine resistance. Both groups of study participants also reported a decrease in the number of sexual partners and increased condom use.

The iPrEx results pertain only to men who have sex with men. Other studies are evaluating the HIV prevention strategy among women, injection drug users, and heterosexual couples in which one partner is infected with HIV and the other is not.


Grant RM, Lama JR, Anderson PL, McMahan V, Liu AY, Vargas L, Goicochea P, Casapía M, Guanira-Carranza JV, Ramirez-Cardich ME, Montoya-Herrera O, Fernández T, Veloso VG, Buchbinder SP, Chariyalertsak S, Schecter M, Bekker LG, Mayer KH, Kallás EG, Amico KR, Mulligan K, Bushman LR, Hance RJ, Ganoza C, Defechereux P, Postle B, Wang F, McConnell JJ, Zheng JH, Lee J, Rooney JF, Jaffe HS, Martinez AI, Burns DN, Glidden DV; iPrEx Study Team. Preexposure chemophrophylaxis for HIV prevention in men who have sex with men. N Engl J Med. 2010 Dec 30;363(27):2587-99.​

Last Updated November 10, 2011

Last Reviewed June 03, 2011