The FDA says patients taking the pill in combination with two other treatments should stop immediately if they develop a rash that grows worse or comes with symptoms like a fever, diarrhea or mouth sores.
Patients taking this drug can develop a rash that covers more than half the body.
Vertex Pharmaceuticals Inc. says the drug's labeling had already warned that patients with a serious skin reaction should stop. The new warning is much more prominent on the label.
Incivek is taken with the pill ribavirin and interferon, which is given by injection. A black box warning is the most serious form of safety warning.