Major
Ciprofloxacin × Haloperidol
Fluoroquinolone antibacterials×First-generation antipsychotics. Butyrophenone derivatives
Mechanism
Dual mechanism: both prolong QT (additively), and ciprofloxacin blocks CYP1A2 – a partial haloperidol clearance route. Haloperidol levels rise.
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
Avoid the combination. Alternative antibiotics: a cephalosporin or nitrofurantoin. Alternative antipsychotics with minimal QT effect: olanzapine or aripiprazole.