Which antiemetic is contraindicated in patients with a history of torsades de pointes?

Droperidol is contraindicated in patients with a history of torsades de pointes primarily due to its potential to prolong the QT interval on the electrocardiogram. Torsades de pointes is a type of polymorphic ventricular tachycardia often associated with a prolonged QT interval, which can lead to serious cardiac events.

Droperidol belongs to the class of butyrophenones, and its use can lead to the development of arrhythmias, especially in susceptible individuals who have pre-existing conditions or factors that may lead to QT interval prolongation. Consequently, this increases the risk of torsades de pointes in these patients.

In contrast, the other antiemetics listed—ondansetron, metoclopramide, and granisetron—generally possess a different safety profile regarding cardiac arrhythmias and are utilized in various clinical scenarios without the same level of concern related to QT prolongation and torsades de pointes. Therefore, droperidol's association with cardiac risks distinguishes it as the appropriate choice in this instance.