Alpha-methyldopa disposition in mothers with hypertension and in their breast-fed infants.

To assess the problem of alpha-methyldopa dosing in lactating mothers with hypertension, we studied three breast-feeding women to determine simultaneous plasma and breast milk concentrations of alpha-methyldopa after a 500 mg oral dose while receiving continuous therapy. Peak excretion of free alpha-methyldopa in breast milk ranged from 0.02 to 1.14 microgram/ml. The breast milk/whole plasma ratios of alpha-methyldopa ranged from 0.19 to 0.34. In two of the three breast-fed infants, plasma levels of alpha-methyldopa were undetectable (less than 0.05 microgram/ml) 6 hours after maternal ingestion of the drug, but in one of these the plasma alpha-methyldopa concentration was 0.09 microgram/ml 10 hours after maternal dosing. It is estimated that when the mother receives 1 gm alpha-methyldopa a day, the maximal cumulative dose of alpha-methyldopa would be 855 micrograms and the average cumulative alpha-methyldopa load to the breast-fed infant would be 195 micrograms, or 0.02% of the maternal dose.