Does the frequency of daily dosage influence compliance with digoxin therapy?

1 The influence of daily dosage frequency on drug compliance has been studied in 80 outpatients for whom maintenance digoxin 0.25 mg daily had been prescribed. 2 Each patient took one tablet (0.25 mg) daily, two tablets (0.125 mg) daily and four tablets (0.0625 mg) daily in randomised order for 2 month periods. 3 Compliance was assessed by tablet counting and by serial measurement of the plasma digoxin concentration. 4 Of the 67 patients (100%) who could have completed the study, 19 (28.4%) were withdrawal for a variety of reasons; in the majority these were consistent with gross non-compliance. 5 The remaining 48 patients (71.6%) took significantly more tablets when prescribed once daily (98.5 +/- 1.0% of the total) or twice daily (96.4 +/- 1.6%) than when given four times daily (92.2 +/- 1.9%). However, there were no significant differences between the plasma digoxin levels obtained at the three dosage frequencies. 6 We conclude that the small improvement in compliance with once or twice daily dosage was clinically unimportant. Dosage frequency did not appear to have a major influence on the grossly non-compliant patients.