Major
Amlodipine × Clarithromycin
Calcium channel blockers (dihydropyridines)×Macrolide antibiotic
Mechanism
Clarithromycin blocks CYP3A4 – the main amlodipine metabolic route. Amlodipine plasma levels rise by 50–60%. Symptomatic hypotension and acute kidney injury have been reported in older patients.
Symptoms
Blood pressure drop: postural dizziness, syncope. Ankle oedema (typical of amlodipine), facial flushing, reflex tachycardia are possible.
Management
During clarithromycin therapy, halve amlodipine and monitor blood pressure. Alternative antibiotics: azithromycin or doxycycline (minimal CYP3A4 effect).