CYP3A4 and torsades de pointes: In July 1996, in a newsletter sent to physicians and pharmacists Health Canada informed that cisaprise was contraindicated in patients taking drugs that inhibited the cytochrome P450-3A4 enzymes that metabolize cisapride or in those taking drugs that could prolong the QT interval since those patients were at increased risk of developing severe ventricular arythmia or torsades de pointe.