Assessing the accuracy of a computerized decision support system for digoxin dosing in primary care: an observational study.

BACKGROUND This study was carried out as part of a European Union funded project (PharmDIS-e+), to develop and evaluate software aimed at assisting physicians with drug dosing. A drug that causes particular problems with drug dosing in primary care is digoxin because of its narrow therapeutic range and low therapeutic index. OBJECTIVES To determine (i) accuracy of the PharmDIS-e+ software for predicting serum digoxin levels in patients who are taking this drug regularly; (ii) whether there are statistically significant differences between predicted digoxin levels and those measured by a laboratory and (iii) whether there are differences between doses prescribed by general practitioners and those suggested by the program. METHODS We needed 45 patients to have 95% Power to reject the null hypothesis that the mean serum digoxin concentration was within 10% of the mean predicted digoxin concentration. Patients were recruited from two general practices and had been taking digoxin for at least 4 months. Exclusion criteria were dementia, low adherence to digoxin and use of other medications known to interact to a clinically important extent with digoxin. RESULTS Forty-five patients were recruited. There was a correlation of 0.65 between measured and predicted digoxin concentrations (P < 0.001). The mean difference was 0.12 microg/L (SD 0.26; 95% CI 0.04, 0.19, P = 0.005). Forty-seven per cent of the patients were prescribed the same dose as recommended by the software, 44% were prescribed a higher dose and 9% a lower dose than recommended. CONCLUSION PharmDIS-e+ software was able to predict serum digoxin levels with acceptable accuracy in most patients.