At least 22 people have suffered serious side effects, including liver failure, from taking an AIDS drug intended to prevent HIV infection after accidental exposure to the virus.
US health agencies have reported that the problems occurred after people took nevirapine, a widely used AIDS drug, after accidentally jabbing themselves with needles or being splashed with infected blood.
The most common reported side effects are liver damage and skin rashes. Nevirapine is marketed by Ohio-based Roxane Laboratories under the name Viramune. The company's website warns that fatal liver damage has been reported in some cases, and recommends liver tests before and during treatment.
Government guidelines do not recommend nevirapine for preventing infection after HIV exposure. But the Centre for Disease Control says doctors may prescribe it because it theoretically works quicker than other AIDS drugs, and it is recommended for preventing AIDS transmission from infected mothers to their babies.
"This makes it very clear that this is a real risk factor," Dr Helene Gayle, the CDC's AIDS chief, said.
The people, mostly health care workers, suffered the side effects between 1997 and 2000, after taking the drug an average of two weeks. None eventually contracted HIV, Gayle said.