Major
Amitriptyline × Ciprofloxacin
Tricyclic antidepressants (TCA)×Fluoroquinolone antibacterials
Mechanism
Additive QT prolongation. Ciprofloxacin additionally blocks CYP1A2 – an amitriptyline metabolic route. Amitriptyline plasma levels rise.
Symptoms
QT prolongation on ECG. Dizziness, syncope, palpitations. Severe cases: polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia and hypomagnesaemia.
Management
Avoid the combination. Alternative antibiotics without QT effect: a cephalosporin or nitrofurantoin. Alternative for neuropathic pain instead of TCA: gabapentin or pregabalin.
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.