Several drugs used in the intensive care unit (ICU) have the potential to prolong the QT interval. If not corrected, this can evolve into the malignant arrhythmia of torsades de pointes. The QT interval is the total duration of depolarization and repolarization of the ventricles; prolonged QT is due to lengthening of the repolarization phase and usually due to changes in potassium handling by sodium or potassium channels. Along QT can be inherited or acquired; the acquired form is usually induced by drugs or electrolyte abnormalities like hypokalemia and hypomagnesaemia.

Drugs commonly used in the ICU that potentiate this effect are haldol, amiodarone, metoclopramide, ibutilide, procainamide, azithromycin, clarithromycin, cisapride, erythromycin, methadone, and pentamidine. When using these drugs, an electrocardiogram (ECG) should be checked to ensure a normal QT.