The Food and Drug Administration has approved the first HIV-prevention pill, a milestone achievement in the ongoing fight against the virus that causes AIDS. Truvada, manufactured by Gilead Sciences Inc., is the first drug that the FDA has approved for reducing risk of infection and will be prescribed as a preventative measure for those who are at high risk of being infected, such as those whose partners already have HIV. The FDA’s decision comes on the heels of three studies published last week in The New England Journal of Medicine, which found daily use of the drug could reduce HIV transmission by as much as 75 percent in heterosexual couples. It was also found to be effective among gay couples. The drug has previously been used to treat HIV, leading researchers to investigate its prevention capabilities.