QT prolongation, torsades des pointes, and cardiac arrest after 4 mg of IV ondansetron.

Ondansetron is a commonly used antiemetic in the emergency department despite a 2011 FDA warning regarding dose-related QTc prolongation and torsades des pointes (TdP). Cases of TdP from small ondansetron doses administered in the emergency department are lacking. A 41-year-old-woman with alcohol use disorder on no medications or supplements presented to an emergency department with one day of nausea, vomiting, and epigastric pain. Examination revealed a pulse of 77 beats/min and epigastric tenderness. The patient received 4 mg IV ondansetron, 30 mg IV ketorolac, and was placed on cardiac monitoring. ECG obtained one minute after ondansetron demonstrated premature ventricular contractions with QTc = 653 ms. Thirteen minutes after receiving ondansetron she suffered TdP and cardiac arrest. She received immediate CPR and IV epinephrine with successful defibrillation at one minute. She then received IV magnesium. Post-arrest ECGs demonstrated persistent QTc prolongation immediately and at three hours post-arrest. Laboratory studies, drawn prior to arrest, demonstrated hypokalemia (3.2 mEq/L), hypomagnesemia (1.3 mg/dL), and elevated lipase (4918 IU/L). She received no additional QT-prolonging agents. Transthoracic echocardiogram and troponins were normal; ECG intervals completely normalized within 12 h and she was discharged neurologically intact. The patient returned 18 months later with recurrent pancreatitis and similar electrolyte abnormalities; QT-prolonging drugs were avoided at that time and her course was uncomplicated. QT prolongation with subsequent torsades des pointes and cardiac arrest may occur in high-risk patients receiving small doses of ondansetron. Further studies are warranted to determine the safest antiemetic for use in the emergency department.