The results of three clinical trials published on Wednesday in the New England Journal of Medicine show that the antiretroviral drug Truvada, a combination of tenofovir and emtracitabine, can be "highly effective at preventing infection in HIV-free individuals -- as long as those individuals take the drug every day as prescribed," CNN's "The Chart" reports (7/11). The strategy of using antiretrovirals to prevent HIV among healthy people at risk of contracting the virus is known as pre-exposure prophylaxis, or PrEP, USA Today notes. "Two studies from Africa in heterosexual patients found that the drugs reduced the rate of HIV infection by 62 percent to 75 percent, a success rate that's comparable to results from studies of gay men," the newspaper writes, adding, "A third study in African women at high risk of infection, however, was ended early after researchers saw the drugs had no effect on HIV rates, largely because fewer than 40 percent of study participants took their pills as instructed" (Szabo, 7/11).