Moderate
Azithromycin × venlafaxine
Macrolides×SNRI (serotonin-norepinephrine reuptake inhibitor)
Mechanism
Additive QT prolongation (venlafaxine prolongs QT at doses above 150 mg).
Symptoms
QT prolongation on ECG. Dizziness, syncope, palpitations. Rarely: polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, and ischaemic heart disease.
Management
For short azithromycin courses (3–5 days) with venlafaxine ≤150 mg, the combination is acceptable. At higher venlafaxine doses or cardiovascular disease: ECG before start or alternative antibiotics.