Plasma digoxin concentrations in patients with atrial fibrillation and indications for the association with other antiarrhythmic agents.

The influence of practolol or verapamil on the activity of digoxin in atrial fibrillation has been studied in 16 hospitalized patients by determining plasma levels of the cardiac glycoside and its effects on the ventricular rate, before and during the association with each of the above drugs. Digoxin alone (0.25 mg/day p.o.) demonstrated a rather feeble activity, giving a satisfactory control of ventricular rate in only 3 patients. The association with low doses of practolol (50 or 100 mg twice a day p.o.) or with verapamil (80 mg three times a day p.o.) clearly improves the effects of digoxin. The action both of practolol and of verapamil is related to the pre-existing ventricular rate, the tachycardic patients being the most sensitive ones.