Drugs that prolong the electrocardiographic QT interval increase the risk of ventricular arrhythmias, particularly torsades de pointes. Ondansetron, a 5-hydroxytryptamine type 3 receptor antagonist antiemetic, is one such drug. We present the cases of 2 patients who were given intravenous ondansetron and subsequently developed torsades de pointes. Both had normal QT intervals at baseline but were discovered to have risk factors that predisposed them to drug-induced QT prolongation and ventricular arrhythmias. We briefly review the mechanisms for torsades de pointes caused by QT-prolonging medications, describe characteristics that increase patients' susceptibility to drug-induced QT prolongation, and call attention to the risk of ventricular arrhythmias in patients who are given ondansetron.
Keywords: Arrhythmias, cardiac/chemically induced; dose-response relationship, drug; drug-related side effects and adverse reactions; electrocardiography/drug effects; emergency treatment; ondansetron/administration & dosage/adverse effects/therapeutic use; product surveillance, postmarketing; risk factors; serotonin 5-HT3 receptor antagonists/therapeutic use; torsades de pointes/chemically induced/physiopathology.