Major
Digoxin × Verapamil
Cardiac glycosides (digitalis)×Non-dihydropyridine calcium channel blocker
Mechanism
Verapamil blocks P-glycoprotein in the intestine and renal tubules – key digoxin clearance routes. Digoxin plasma levels rise by 50–75%. Verapamil also slows AV conduction.
Symptoms
Nausea, anorexia, visual disturbances (yellow-green halos around lights), arrhythmias ranging from premature beats to ventricular tachycardia. Older adults: confusion, dizziness. Symptoms appear within 1–2 weeks of co-administration.
Management
When verapamil starts, reduce digoxin by 30–50%; check level at 1 week. Alternative calcium channel blocker without P-glycoprotein effect: amlodipine (for blood pressure control) or a beta-blocker.