PROLONGATION OF THE QT INTERVAL RELATED TO CISAPRIDE-DILTIAZEM INTERACTION

Cisapride, a cytochrome P450 3A4 (CYP3A4) substrate, is widely prescri bed for the treatment of gastrointestinal motility disorders. Prolonga tion of QT interval, torsades de pointes, and sudden cardiac death hav e been reported after concomitant administration with erythromycin or azole antifungal agents, but not with other CYP3A4 inhibitors. A possi ble drug interaction occurred in a 45-year-old woman who was taking ci sapride for gastroesophageal reflux disorder and diltiazem, an agent t hat has inhibitory effect on CYP3A4, for hypertension. The patient was in near syncope and had QT-interval prolongation. After discontinuing cisapride, the QT interval returned to normal and symptoms did not re cur. We suggest that caution be taken when cisapride is prescribed wit h any potent inhibitor of CYP3A4, including diltiazem.