Major
Ciprofloxacin × Escitalopram
Fluoroquinolone antibacterials×Selective serotonin reuptake inhibitors (SSRIs)
Mechanism
Additive QT prolongation. Escitalopram prolongs QT dose-dependently (FDA Lexapro caps at 20 mg/day); ciprofloxacin contributes more weakly but additively.
Symptoms
QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes) with risk of ventricular fibrillation and sudden cardiac death. Risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, and ischaemic heart disease.
Management
During ciprofloxacin therapy, cap escitalopram at 10 mg/day. Alternative antibiotics: a cephalosporin or nitrofurantoin (no QT effect).