Major
Amiodarone × Haloperidol
Class III antiarrhythmics (Vaughan Williams)×First-generation antipsychotics. Butyrophenone derivatives
Mechanism
Additive QT prolongation, especially with parenteral (IV) haloperidol. Torsades de pointes and fatal arrhythmias have been reported, especially in ICU patients with hypokalaemia.
Symptoms
QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes) with risk of ventricular fibrillation and sudden cardiac death. Risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, and ischaemic heart disease.
Management
Avoid the combination, especially IV haloperidol. Alternative antipsychotics with minimal QT effect: olanzapine or aripiprazole. For acute delirium in amiodarone patients: dexmedetomidine (no QT effect).