(Jeff Chiu | The Associated Press) In this May 10, 2012, file photo, a doctor holds Truvada pills at her office in San Francisco. New research shows more promise for using AIDS treatment drugs, such as Truvada, as a prevention tool, to help keep uninfected people from catching HIV during sex with a partner who has the virus. Truvada has been shown to help prevent infection when one partner has the virus and one does not, but the evidence so far has been strongest for male-female couples.