Assessment of Digoxin Serum Concentration in Continuous and Interrupted Digoxin Regimens.

Abstract: Since digoxin possesses a narrow therapeutic index and shows a large interpatient pharmacokinetic variability, serum digoxin monitoring is a suitable guideline for optimization of digoxin therapy. However, digoxin concentration monitoring is not always accessible; and as result sometimes in order to prevent digoxin toxicity a drug holiday is performed (the drug is off for 1 or 2 days a week). In this investigation a prospective cohort study was designed to evaluate drug regimen. One hundred and twenty three inpatients receiving digoxin for heart failure or atrial were included in this study. In the group with a drug holiday regimen, 3 samples of serum were taken from each patient. (Preholiday trough, 6-8 hrs after the last dose in steady state, post holiday trough). In other groups 2 samples were collected (trough and 6-8 hrs after the last dose in steady state) and samples were assayed by radioimmunoassay. The results showed that 73.33% of patients receiving 0.125 mg/day had a level less than 0.8 ng/ml (sub therapeutic). While most patients had preholiday concentration within therapeutic range (0.8-2 ng/ml), due to the concentration fluctuation, clinical ineffectiveness of this drug regimen is questionable. In patients with 0.25 mg/day regimen, 62.5% of had therapeutic level and an appropriate clinical response. While a population pharmacokinetic analysis must be designed for a proper decision about the dosage adjustment in patients of this study in future, it seems that 1 tablet/day regimen is preferred.