HIV-negative persons taking antiretrovirals for postexposure prophylaxis–prevention of infection immediately after a needlestick or sexual exposure to HIV–should avoid using nevirapine except in unusual situations, according to recommendations published in the January 5 MMWR (Morbidity and Mortality Weekly Report) by the U.S. Centers for Disease Control and Prevention (CDC). Nevirapine has not been officially recommended for this use, but physicians have used it because of its rapid action and success in preventing mother to infant transmission.