Snapshot A 60-year-old man with a past medical history of psoriasis, hypertension, and diabetes presents to the emergency room for nausea and vomiting. He has 3 episodes of nonbloody, non-bilious emesis. An electrocardiogram shows that he has borderline prolonged QT interval. His physician would like to give him an anti-emetic, but decides to avoid ondansetron due to its QT prolongating effect. Introduction Drugs ondansetron Mechanism of action serotonin (5-HT3) receptor antagonist, which decreases vagal stimulation Clinical use anti-emesis particularly in the setting of chemotherapy or procedure Adverse effects QT prolongation serotonin syndrome headache constipation