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

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.

Digoxin use in the elderly

The current extensive use of digoxin in elderly patients with left ventricular failure and sinus rhythm may not be clinically justifiable; in a significant proportion of these patients the frequency of digitalis toxicity may outweight the therapeutic benefits of the drug. When digoxin is used in elderly patients, the specific geriatric pharmacology of the drug must be considered. Clinical benefit should be documented before proceeding to long-term maintenance therapy. In selected elderly patients, withdrawal of digoxin with careful follow-up may be a worthwhile procedure. Studies are needed comparing the relative benefits and toxicities of digoxin versus diuretics in the management of heart failure in the elderly.

Comparison of two different loading doses of digoxin in severe renal impairment

The correct loading dose of digoxin in patients with advanced renal failure is still a matter of discussion. The effects has been studied of loading doses of digoxin 0.625 mg or 1.25 mg given over 48 h according to randomized crossover design to healthy volunteers and to two different groups of patients with renal impairment and the same mean endogenous creatinine clearance of about 15 ml/min. The subsequent maintenance dose for 4 days was digoxin 0.25 mg in the volunteers and 0.125 mg in both groups of patients. The minimum plasma digoxin concentrations before each dose was measured by radioimmunoassay and the plasma levels in the different groups have been compared. In the healthy volunteers no significant difference was found during the study, despite wide variation in the plasma digoxin concentration. In contrast, in patients with renal failure, the group with the higher loading dose showed significantly higher plasma concentrations 24, 36 and 48 h after drug administration, reaching the highest mean value of 2.2 ng/ml at 48 h. However, after 120 h of maintenance therapy a mean digoxin concentration of 1.3 ng/ml was found in both groups. Thus, despite different loading doses identical plasma concentrations were reached during administration of the same maintenance therapy. The higher plasma digoxin concentration obtained during administration of a higher loading dose might be the cause of arrythmias in individual patients.