A simple aid to digoxin prescribing.

We have designed a simple nomogram for predicting digoxin dosage and have tested it prospectively in two consecutive studies. These were both conducted in hospital inpatients who were not already taking digoxin but who required drug therapy for atrial tachyarrhythmias and/or cardiac failure. Study I. Sixty-seven patients received digoxin according to the nomogram and 50 completed the ten day course of the study. Forty-one of these patients were eligible for the final analysis. On the tenth day of treatment, 28 patients were within the therapeutic range for plasma digoxin (0.8 to 2.0 ng.ml-1), 12 were subtherapeutic (less than 0.8 ng.ml) and one was potentially toxic (greater than 2.0 ng.ml-1). Study II. Thirty patients completed the second study. Digoxin was prescribed according to the nomogram with the addition of a dosage correction based on the plasma digoxin level on Day 3. On the tenth day of treatment, 24 patients were within the therapeutic range, one in the subtherapeutic and 5 in the potentially toxic. This simple digoxin nomogram, with or without the Day 3 dosage correction, should prove to be a useful aid to prescribing in patients who do not require rapid digitalisation. It is particularly relevant to elderly inpatients with atrial tachyarrhythmias and/or cardiac failure.