Transfer of antibiotics into maternal milk

Thirty antibiotics, including penicillins, cephems, chloramphenicol, tetracyclines, macrolides, and aminoglycosides, were given p.o., i.m. or i.v. once to 70 puerperal women to compare milk drug levels with serum levels over a 6-h period. Antibiotic transfer into the milk was small. No drugs except for a few (chloramphenicol, tetracyclines, macrolides) reached the level of 1 mcg/ml or greater. Penicillins and cephams detected in trace amounts in the milk are likely to have little effect on infants.