The FDA announced that a single 32-mg intravenous dose of ondansetron should be avoided because it can prolong the QT interval and can predispose patients to develop polymorphic ventricular tachycardias (torsades de pointes).
Ondansetron is a 5-HT3 receptor antagonist approved as an antiemetic (to treat nausea and vomiting) in patients treated with emetogenic cancer chemotherapy or after surgery. Ondasetron-induced QT prolongation is dose-dependent: 6 and 20 ms after a single intravenous dose of 8 and 32 mg, respectively. Therefore, the FDA recommended to conduct a thorough study to determine the QT prolongation induced by ondansetron. The prolongation of the QT interval may be higher in patients with congenital long QT syndrome, hypokalemia, congestive heart failure, or bradyarrhythmias, or taking QT prolonging drugs. Thus, it is recommended to use no single intravenous dose exceeding 16 mg.