Moderate
Amitriptyline × Azithromycin
Tricyclic antidepressants (TCA)×Macrolides
Mechanism
Azithromycin weakly prolongs QT, additively with the TCA amitriptyline (a pronounced QT prolonger). Clinically significant arrhythmia is rare in young patients without cardiovascular disease.
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) in young patients, the combination is acceptable. In older patients, cardiac disease, or hypokalaemia: ECG before start, alternative antibiotics (doxycycline, a cephalosporin), or replace amitriptyline with gabapentin/pregabalin for neuropathic pain.