Major
Clarithromycin × Escitalopram
Macrolide antibiotic×Selective serotonin reuptake inhibitors (SSRIs)
Mechanism
Both prolong QT, and clarithromycin blocks CYP3A4 (a minor escitalopram metabolic route). Escitalopram levels rise moderately. In patients with hypokalaemia or other arrhythmia risk factors, torsades de pointes risk increases.
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 where possible. Alternative antibiotics: azithromycin (with caution given its own QT risk) or doxycycline. During clarithromycin therapy, cap escitalopram at 10 mg/day.