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The epidemiology of prescribing long-term digoxin was studied in 241 patients from six group general practices. Each patient was assessed for the initial reason for prescribing digoxin and present clinical status, and the serum digoxin concentration was measured between six and 12 hours after the previous dose.
The results show that digoxin was most commonly prescribed for elderly patients; 90% of patients were aged 60 years or more. The reasons for prescribing digoxin were considered adequate in only 55% of the total group; 71% of the patients were judged to be clinically well and 75% of the 95 patients with atrial fibrillation had ventricular rates of less than 90 beats per minute. `Therapeutic' serum digoxin concentrations (0.8—2.0 ng ml-1) were observed in only 48% of patients; the level was sub-therapeutic in 46% and potentially toxic in 6%. No clear-cut relationship was found between clinical well-being and serum digoxin concentration. The type of supervision (whether hospital or general practice) did not affect appropriateness of prescribing, clinical well-being or likelihood of achieving a therapeutic serum digoxin level.
This study would suggest the need for critical review of digoxin therapy in all patients who are taking it long-term. In some patients its continuance would appear unnecessary; in others, efficacy may be improved either by dose adjustment or by ensuring compliance. On occasions, particularly in patients with sinus rhythm, measurement of serum digoxin concentrations may prove helpful in this evaluation.