Major
Azithromycin × Dronedarone
Macrolides×Class III antiarrhythmic
Mechanism
Additive QT prolongation. Azithromycin received a dedicated FDA warning in 2013 for fatal ventricular arrhythmia risk. Dronedarone itself prolongs QT, and combined the effects add up.
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. Alternative antibiotics: doxycycline or a cephalosporin (no QT effect). If azithromycin is needed, ECG before start and potassium and magnesium in range.