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

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 the first appearance of toxic symptoms 'steady state' values of about 6 ng digoxin/ml werefound. Excluding one divergent patient, a close inverse correlation wasfound 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.