Secretion of methotrexate into human milk

After oral administration to a lactating patient with choriocarcinoma, the cancer chemotherapeutic agent methotrexate (MTX) was found to be excreted in milk at low but readily detectable levels. The highest milk:plasma concentration ratio, 0.08:1, was observed 10 hr. after administration of the drug. The kinetics of the MTX secretion process correspond to those which would be anticipated for a weak organic acid transferred from plasma to milk by passive diffusion of the nonionized form. © 1972.