Placental transfer and fetal uptake of 3H-digoxin in humans.

Placental transmission and fetal distribution of 3H-digoxin were studied in seven pregnant women undergoing legal termination of pregnancy during the first half of gestation. The radioactivity in fetal and maternal plasma and in fetal tissues was estimated using the oxidation method, and the integrity of the labelled drug by thin layer chromatography. The 3H-digoxin activity was clearly demonstrated in the umbilical cord blood five minutes after injection of the drug into the maternal blood, and the fetal plasma concentrations of 3H-digoxin approximated to the maternal value 30 minutes after drug administration. The distribution of 3H-digoxin in the fetal tissues was relatively even, with the highest 3H concentrations found in the heart and placenta, the lowest in the brain. The results suggest that the capacity of human fetal heart to bind digoxin during the first half of gestation is limited.