Torsades de pointes in two chronic renal failure patients treated with cisapride and clarithromycin.

Patients with chronic renal failure are often on multiple medications and are at risk for the development of adverse effects from drug interactions. Two cases of torsades de pointes that followed the initiation of clarithromycin therapy in patients receiving long-term cisapride therapy are being reported. Elevated cisapride levels while on this combination with return to therapeutic range while on cisapride only was documented in one of the patients. The role of the inhibition of cytochrome P-4503A4 in the occurrence of the arrhythmia is discussed.