Estimation of serum digoxin levels in geriatric patients

The correlation in geriatric patients between estimated serum digoxin levels based on pharmacokinetic calculations and serum digoxin levels measured by radioimmunoassay was studied. Serum digoxin levels were estimated for 17 geriatric patients recieving digoxin using the "total body stores" concept. A statistically significant correlation between calculated and measured digoxin levels was shown (p less than 0.05, r = 0.51); however, 95% confidence limits were so large (+/- 1.75 ng/ml) that the results were clinically unacceptable. Until data describing specific causes of variance are available and calculations modified to account for specific variations, pharmacokinetic models should not be relied upon for accurate estimates of digoxin levels in geriatric patients.