Kinetics of the translactal passage of digoxin from breast feeding mothers to their infants

In order to find out whether digoxin therapy of nursing mothers might produce discomfort in suckling infants we have investigated the kinetics of the transfer of digoxin from plasma to milk in 11 nursing mothers. After intravenous or oral application of a single dose of 0.5 mg or 0.75 mg digoxin simultaneous serum, fore- and hindmilk samples were taken. Obviously, a rapid equilibrium occurred between the serum and the milk compartments and there was no difference between fore- and hindmilk. All three digoxin concentration profiles ran parallel with a milk to serum ratio of 0.6 to 0.7. The curves could best be fitted by the sum of two exponential functions. For predicting the digoxin intake into the suckling infant, simulations were carried out on the basis of two coupled compartment models. When the kinetic milk data as well as the kinetic data obtained in infants were fitted by this model it could be shown that even in the case of long half-lives only about 3% of the therapeutic drug levels were reached in the baby. Thus, one can conclude that digoxin accumulation to toxic concentrations should not occur in infants of women treated with appropriate doses of digoxin.