Distribution of methylergometrine in the breast milk of dogs.

Distribution of methylergometrine maleate (MEM) was determined in plasma and milk of lactating beagle dogs after a single intravenous and oral dose and after prolonged administration. Plasma and milk levels were measured by a radioimmunoassay. MEM was found to be excreted into milk rapidly. The equilibrium between plasma and milk concentrations was reached at 30 min after intravenous and at 60 min after oral administration. The milk : plasma concentration ratio over post distribution period was one. The kinetics of MEM secretion process correspond to those which would be anticipated for a weak organic base transferred from plasma to milk by passive diffusion of the nonionized form.