Value of serum digoxin concentration measurement in the control of digoxin therapy in atrial fibrillation.

The association between steady-state serum digoxin concentrations and control of ventricular response rate (VRR) was studied in 53 consecutive patients with atrial fibrillation. Decreases in VRR were significantly correlated with serum digoxin (rs = -0.22, P less than 0.05). Clinical responses were appropriate to serum digoxin concentrations in 37 patients (69.8%) and were inappropriate in 16 (30.2%) (P less than 0.05). Complicating clinical factors were present in all eight patients with inappropriate responses to therapeutic serum digoxin (0.5 to 2.0 ng/ml) (P = 0.046), but were also found in many patients with appropriate responses and thus could not serve to differentiate between the two categories. Digitalis intoxication occurred in one of the three patients with a concentration of serum digoxin greater than 2 ng/ml (P = 0.056). In 30% of our patients with atrial fibrillation, monitoring of serum digoxin was of value in identifying inappropriate therapeutic responses indistinguishable by clinical means and in defining the subgroup of refractory cases, which allows the prevention of digitalis intoxication.