Torsades de pointes due to drug interaction between disopyramide and clarithromycin.

Torsades de pointes (TdP) is polymorphic ventricular tachycardia occurring in the setting of a prolonged cardiac repolarization. Drug interactions between macrolide antibiotics such as erythomycin and pharmacologic agents that prolong the QT interval have been known to cause TdP. However, clarithromycin is thought to be less frequently associated with drug induced TdP, because it inactivates hepatic cytochrome P-450 to a lesser extent than erythromycin. We describe a case of TdP caused by a drug interaction in a 76-year-old woman taking long-term disopyramide after she was given clarithromycin concomitantly for chronic bronchitis.