Major
Ciprofloxacin × citalopram
Fluoroquinolone antibacterials×SSRI (selective serotonin reuptake inhibitor)
Mechanism
Additive QT prolongation (both prolong QT). Ciprofloxacin weakly blocks CYP1A2; citalopram is metabolised by CYP2C19, so the pharmacokinetic effect is minimal. The main risk is additive QT.
Symptoms
QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, and ischaemic heart disease.
Management
Alternative antibiotics: a cephalosporin or nitrofurantoin (no QT effect). If ciprofloxacin is needed: ECG before start, maintain potassium and magnesium, keep citalopram at 20 mg.