Transfer of digoxin across the placenta and into breast milk.

Eleven mothers given digoxin throughout pregnancy because of rheumatic heart disease were studied. Digoxin was identified in the placenta and, for the first time, in milk. Paired cord and maternal blood samples obtained at parturition showed lower digoxin levels in cord blood than in maternal blood. The total tissue-bound digoxin level in the placenta correlated closely with maternal digoxin levels. These findings suggest strongly the presence of a placental barrier for digoxin. Similar digoxin concentrations (0.825 +/- 0.015 nmol/l) were found in milk samples obtained daily between the third and seventh days post partum. The half-life of digoxin in the newborn was 36.2 +/- 5.43 hours (Mean +/- SEM); thus all the digoxin present at birth would be excreted within 10 to 11 days.