The condition was seen almost immediately in six of the patients. Three of the nine required the placement of a pacemaker and seven had also been taking a beta blocker, which slows heart rates.
The labels on the hepatitis C drugs already contain a warning against co-administration with amiodarone and particularly in patients also taking beta blockers. AbbVie’s rival hepatitis C treatment Viekira Pak carries a similar warning.
“We believe this disclosure will have little or no effect on demand for Harvoni and Sovaldi,” Sanford Bernstein analyst Geoffrey Porges said in a research note.
“First, the underlying patient numbers on amiodarone are relatively small. Second, there is no inherent reason that hepatitis C-infected individuals should have much higher rates of treatment with amiodarone, so the exclusion of co-administration is unlikely to materially affect the dynamics of the market,” he said.
Gilead, in a statement, said “it remains confident in the safety profiles of Sovaldi and Harvoni” and will continue to monitor their safety in collaboration with health regulators and the medical community.
Amiodarone is an older drug used to keep the heart beating normally in patients with life threatening rhythm disorders, such as ventricular tachycardia or ventricular fibrillation. It has a history of potentially dangerous toxicities.
The new hepatitis C drugs represent a major breakthrough as they can cure well over 90 percent of patients who have the liver destroying virus with virtually none of the troubling side effects of older treatments.
Gilead shares were down $2.05, or 2 percent, at $100.24 on Nasdaq.
(Reporting by Bill Berkrot; Editing by Tom Brown)