Major
Digoxin × Verapamil
Cardiac glycosides (digitalis)×Non-dihydropyridine calcium channel blocker
Mechanism
Verapamil inhibits P-glycoprotein, which clears digoxin via kidney and intestine. Digoxin plasma concentration rises 50–75%. Digoxin has a narrow therapeutic index (target 0.5–0.9 ng/mL, toxic above 2). Verapamil also amplifies digoxin's bradycardia and AV block.
Symptoms
Nausea, vomiting, visual disturbances (yellow halos), bradycardia below 50, AV blocks, ventricular arrhythmias.
Management
When starting verapamil, reduce digoxin by 30–50% and check level on days 5–7. Alternative calcium channel blocker: amlodipine, which does not inhibit P-glycoprotein. Avoid the combination in the elderly.
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.