Azithromycin × Dronedarone

Both drugs prolong the QT interval. Dronedarone prolongs the corrected QT interval (QTc) by about 10 ms (dronedarone SmPC). The azithromycin SmPC reports QT prolongation and torsades de pointes with macrolides, azithromycin included. The effects add up, and the dronedarone SmPC warns that proarrhythmic effects may occur when it is combined with drugs that favour arrhythmias or with potassium and magnesium disorders.

QT prolongation on the electrocardiogram (ECG) causes no symptoms by itself. Palpitations, dizziness or fainting may occur. The dangerous complication is torsades de pointes, a ventricular tachycardia that can end in cardiac arrest (azithromycin SmPC). The risk is higher in women and older people, with low potassium or magnesium, marked bradycardia or severe heart failure (azithromycin SmPC).

The dronedarone SmPC contraindicates it with drugs that can induce torsades de pointes and lists some oral macrolides, such as erythromycin; azithromycin is not named on that list (dronedarone SmPC). The azithromycin SmPC asks for caution in patients on class III antiarrhythmics, dronedarone among them, and in anyone taking QT-prolonging drugs (azithromycin SmPC). The azithromycin label approved by the US Food and Drug Administration (FDA) advises weighing the risk of fatal QT prolongation in these patients (azithromycin FDA label). If azithromycin is still given with dronedarone, potassium and magnesium deficits are corrected before and during treatment, the electrocardiogram (ECG) is checked during treatment, and dronedarone is stopped if the corrected QT interval (QTc) reaches 500 ms or more (dronedarone SmPC).