Use of digoxin in infants and children, with specific emphasis on dosage.

The foregoing discussion leads to several general conclusions regarding the use of digoxin in the pediatric patient. First, pharmacokinetic studies indicate that somewhat higher doses are required in the infant to attain the same serum levels as in the adult. Important sources for this difference appear to be more rapid body clearance of digoxin and larger volume of distribution in the infant. Second, higher serum digoxin levels are not indicated on the basis of decreased myocardial uptake of digoxin in the infant. Tissue uptake of digoxin, as indicated by myocardium/serum digoxin ratios, is higher in infants and children than in adults. Third, according to results of animal studies, the inotropic sensitivity to digoxin in the young is probably greater--certainly not less--than in the adult. This is opposite to a commonly held view that the immature heart is less sensitive to cardiac glycosides and therefore requires higher serum levels for a therapeutic effect. Rather, the infant has decreased sensitivity of the conduction system to digitalis toxicity, and healthy myocardium less prone to arrhythmia than the adult. Therefore the infant may tolerate, but does not require, higher serum levels of digoxin. Fourth, high levels of serum digoxin (greater than 2 ng/ml) are not associated with greater inotropic effects in the pediatric patient. The higher dosages of digoxin are, instead, associated with greater frequency of toxic effects, especially in infants receiving concomitant diuretic therapy. Therefore, a digoxin dosage recommendation is presented, that will result in mean serum digoxin levels of 1.1 to 1.7 ng/ml.(ABSTRACT TRUNCATED AT 250 WORDS)