Myocardial vs serum digoxin concentrations in infants and adults.

To establish whether there is a difference between infants and adults in the relationship of serum levels of digoxin to dosage or the ratio of myocardial to serum digoxin levels, the concentrations of digoxin in right atrial appendage (RAA) and serum were measured in 12 infants and 17 adults undergoing open heart surgery. Although the daily digoxin dose per weight for the infant was significantly greater than that for adults, there was no difference in the serum digoxin levels for the two groups. We found, however, a considerable difference in myocardial digoxin levels. The RAA digoxin levels were 211.8 +/- 72.1 ng/g of wet weight in infants and 35.1 +/- 7.7 ng/g of wet weight in adults. Similarly, the RAA-serum digoxin ratio was much higher in infants (149 +/- 30) than in adults (28 +/- 5). These data indicate discrepancies between infants and adults in the pharmacokinetics of digoxin, especially with respect to myocardial uptake.