Can digoxin prescribing be improved? A comparison between intuitive and assisted dose selection

Abstract

37 patients on maintenance digoxin therapy were observed in hospital over an 8 day period. From day 1 to day 8 measurements of plasma digoxin and serum creatinine indicated that these patients were in the equilibrium state with regard to digoxin levels and renal function. Assuming a linear relationship between dose and plasma concentration, it was possible to calculate the doses which would have produced plasma concentrations of 1.5 ng/ml, and at the limits of the ‘usual therapeutic range’, 0.8 and 2.0 ng/ml. Doses obtained from six prescribing aids and those prescribed intuitively by the doctor were then compared. None of the methods used would have resulted in plasma digoxin concentrations within the ‘usual therapeutic range’ in more than 57% of the patients. The physicians' intuitive choice appeared to be better than the doses estimated from prescribing aids, in that they were correct as often as any assisted method, and when wrong tended to prescribe ‘too low’ rather than ‘too high’. The prescribing aids tended to overestimate dosage in many patients, as high as 65% with one. Plasma digoxin concentration measurement would appear to be the only way to ensure adequate therapeutic efficacy and avoid toxicity in patients receiving maintenance digoxin.