Serum Digoxin Concentrations in the Human Fetus, Neonate and Infant

The correlation between digoxin dosage and serum digoxin concentration measured by radioimmunoassay was investigated in seven neonates (three to 30 days of age) and 10 infants (one to 12 months of age) with congenital heart disease. The results were compared with those from 21 adult patients. Digoxin dosages commonly used in the neonates and infants were substantially larger than those used in adults on a basis of milligrams per kilogram of body weight or milligrams per square meter of body-surface area. This higher dosage schedule produced a mean serum digoxin concentration five to eight hours after the last maintenance dose of 2.0 ± 0.9 (± S.D.)ng per milliliter in children, a value significantly higher than that of the adults (1.3 ± 0.4) (p less than 0.005). Despite the higher concentration, which ranged up to 4.3 ng per milliliter, no case of cardiac-rhythm disturbance suggesting digoxin intoxication was observed. In each of seven women who received digitalis during pregnancy, fetal umbilical-cord concentrations were similar to those in maternal venous blood, documenting transplacental passage of the drug.