In response to postmarketing case reports and case-control studies, the labeling of the typical antipsychotic haloperidol (Haldol) now bears a strengthened warning concerning its capability of inducing prolongation of the QT interval and torsades de pointes, a lethal ventricular tachycardia. The incidence of the possibly fatal adverse effects appears to be greatest when the drug is administered intravenously or at doses higher than those recommended.

Although haloperidol is not approved for IV administration, such off-label use appears to be fairly common clinical practice in certain settings. Additionally, the warning informs health care providers that any formulation of haloperidol should be administered with particular caution in patients who have other conditions that prolong the QT interval (such as hypokalemia and hypomagnesemia), underlying cardiac abnormalities, hypothyroidism, or genetic long QT syndrome and in patients who are taking other drugs known to prolong the QT interval. If haloperidol is administered intravenously, a cardiac monitoring protocol should be implemented and observed.