Plasma digoxin concentration--its relation to digoxin dosage and clinical effects in patients with atrial fibrillation.

With a modified, precise 86Rb methodplasma digoxin concentration was estimated in patients with atrialfibrillation. They received successively increasing digoxin doses until they began to develop symptoms of digitalis intoxication. The dosage was changed every 14th day. A high correlation was found between digoxin dosage and plasma digoxin concentration. Patients who did not develop symptoms of digitalis intoxication until at high doses showed a slower increase ofplasma levels. At thefirst appearance of toxic symptoms 'steady state' values of about 6 ng digoxin/ml were found. Excluding one divergent patient, a close inverse correlation was found between plasma digoxin concentration registered at o0375 mg/day and the 'optimal' doses or the toxic limit of the patients. With a plasma digoxin assay a prediction of an adequate digoxin dosage may thus be possible. Though a poor correlation was found between ventricular rate and plasma digoxin concentration there was a good relation between the clinical effects of the glycoside and the plasma concentration; the 'optimal' digoxin effect was obtained at a fairly constant level of digoxin in plasma.