Drug interactions between Calan and Lanoxin

ADJUST DOSE: Verapamil increases digoxin levels significantly in most patients. Verapamil decreases renal and extrarenal clearance of digoxin. Serum digoxin levels may increase by 50% to 75% during the first week of concomitant verapamil therapy. Increases may be larger in patients with hepatic cirrhosis. Digoxin and verapamil have additive effects in slowing AV conduction. In clinical trials with digitalized patients with atrial fibrillation or atrial flutter, 15% of patients developed ventricular rates of less than 50/min and 5% developed asymptomatic hypotension.

MANAGEMENT: If verapamil and digoxin are used together to control a supraventricular tachyarrhythmia, the dosage of each drug may have to be reduced. Despite the possible negative inotropic effects of verapamil, digoxin dosage probably will not have to be increased when a patient with congestive heart failure is given verapamil. Increased digoxin concentrations may offset the negative inotropic effects of verapamil. Patients should be closely monitored for clinical and laboratory evidence of digoxin safety and efficacy while taking verapamil and evaluated for underdigitalization when verapamil is discontinued. Patients should be advised to notify their physicians if they experience signs of toxicity such as nausea, anorexia, visual changes, slow pulse, or irregular heartbeats. Calcium channel blockers such as felodipine, or amlodipine, isradipine, and nicardipine appear to affect digoxin levels to a lesser extent or not at all and may be considered as alternatives.