Effect of intravenous ondansetron on QT interval prolongation in patients with cardiovascular disease and additional risk factors for torsades: a prospective, observational study

BACKGROUND The 5-hydroxytryptamine type 3 antagonists, or setrons (eg, ondansetron), are commonly used for nausea and vomiting in the hospital setting. In 2001, droperidol was given a black box warning because it was found to prolong the QT interval and induce arrhythmias. The setrons share with droperidol the same potential proarrhythmic mechanisms, but limited data exist concerning their effects on the QT interval in individuals at high risk for torsades de pointes. METHODS Forty hospitalized patients admitted for heart failure or acute coronary syndromes with one or more risk factors for torsades de pointes and an order for intravenous ondansetron 4 mg were enrolled in this prospective, observational study. The QT interval corrected for heart rate (QTc) was obtained via a 12-lead electrocardiogram on admission and again 120 minutes after the first dose of ondansetron in order to determine the mean change in QTc following ondansetron exposure. RESULTS The mean time interval between obtaining the baseline electrocardiogram and the second electrocardiogram following ondansetron administration was 3.5 ± 2.14 hours. In the total population, the QTc interval was prolonged by 19.3 ± 18 msec (P < 0.0001) 120 minutes after ondansetron administration. For patients with an acute coronary syndrome and those with heart failure, QTc was prolonged by 18.3 ± 20 msec (P < 0.0001) and 20.6 ± 20 msec (P < 0.0012), respectively. Following ondansetron exposure, 31% and 46% in the heart failure and acute coronary syndromes groups, respectively, met gender-related thresholds for a prolonged QTc. CONCLUSION Our study found QTc prolongation due to ondansetron administration similar to that found in previous studies. When used in patients with cardiovascular disease (eg, heart failure or acute coronary syndromes) with one or more risk factors for torsades de pointes, ondansetron may significantly increase the QTc interval for up to 120 minutes after administration. From a patient safety perspective, patients who are at high risk for torsades de pointes and receiving ondansetron should be followed via telemetry when admitted to hospital.