To : Susan Pszenitzki Re : Antibiotics in breast milk To answer your question as to how long it takes for antibiotics to enter milk, almost immediately, maybe 1 hour at most. But the levels are extremely low for amoxicillin ( < 0.7% of the maternal dose). As to how long it is resident in milk after discontinuing, perhaps 12-24 hours at very very small levels. Unless your child is allergic to penicillin, I seriously doubt any observed symptoms were due to the amoxicillin you took. Tom Hale