Major
Dronedarone × Quetiapine
Class III antiarrhythmic×Atypical antipsychotics
Mechanism
Additive QT prolongation (both prolong QTc). Dronedarone carries an FDA boxed warning for QT risk.
Symptoms
QT prolongation on ECG. Dizziness, syncope, palpitations. Severe cases: polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia and hypomagnesaemia.
Management
Avoid the combination. Alternative antipsychotics with minimal QT effect: olanzapine or aripiprazole. Alternative antiarrhythmic: a beta-blocker for rate control or catheter ablation.