Moderate
Azithromycin × Quetiapine
Macrolides×Atypical antipsychotics
Mechanism
Additive QT prolongation (quetiapine prolongs QT at high doses).
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 quetiapine ≤300 mg, the combination is acceptable. On high quetiapine doses or cardiovascular disease: ECG before start or alternative antibiotics.