Major
Dronedarone × Mirtazapine
Class III antiarrhythmic×Other antidepressants (NaSSA)
Mechanism
Mirtazapine prolongs QT dose-dependently (especially above 30 mg/day). Combined with dronedarone, torsades de pointes risk rises.
Symptoms
QT prolongation on ECG. Dizziness, syncope, palpitations. Severe cases: polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia and hypomagnesaemia.
Management
The combination is acceptable at low mirtazapine doses (≤30 mg/day) and normal potassium. ECG before start and at 2 weeks. Alternative antidepressants with minimal QT effect: agomelatine or sertraline (up to 100 mg).