Dose and administration of IV ondansetron
ECG interval changes, including prolongation of the QTc interval, are a class effect of the first-generation serotonin antagonists, including ondansetron; potentially fatal cardiac arrhythmias may result. QTc prolongation occurs in a dose-dependent manner, and is expected to be greater with faster rate of infusion and larger doses for intravenous (IV) administration. Revised ondansetron labeling in the US includes a recommendation to limit single IV doses to no more than 16 mg. Canadian guidelines that took effect in June 2014 place additional dosing restrictions on IV ondansetron to mitigate the risk of QT prolongation, particularly in older adults, in whom the initial dose should not exceed 8 mg .
hc-sc/2014/39943a-eng.php (Accessed on June 16, 2014).