Late last week Gilead Sciences issued a warning about a rare but potentially fatal interaction between its stellar new hepatitis C drug sofosbuvir and amiodarone, a potent but tricky antiarrhythmic agent. Sofosbuvir is marketed as Sovaldi and, in combination with another antiviral agent, as Harvoni. Amiodarone, which is used to treat dangerous heart rhythm problems, has a number of different side effects and an extremely long half-life. Its use is generally reserved for difficult cases.
Gilead reported nine cases of symptomatic bradycardia (slow heart rate). One patient died of a cardiac arrest and 3 patients received a pacemaker. Six cases occurred during the first day of treatment with sofosbuvir. Several patients were taking additional antiviral agents and 7 patients were also taking a beta blocker. The company said the mechanism of action for the interaction is unknown.
Paul Sax, an infectious diseases specialist at the Brigham and Women Hospital, said that “this is a very uncommon drug drug interaction. In the short-term, I anticipate it will have almost no effect on prescribing practices.”
A Baird analyst also said it is unlikely that the news will have a significant impact on the use of sofosbuvir. He estimated that there were about 1,000 patients taking amiodarone among the more than 200,000 patients who have received sofosbuvir so far. He noted that the baseline bradycardia risk for amiodarone by itself is about 2.5% per year.
The company said that the coadministration sofosbuvir and amiodarone is not recommended. In cases where there is no alternative to coadminstration Gilead recommends close cardiac monitoring of patients, including monitoring in the hospital for the first 48 hours of treatment.