Excretion into breast milk is not significant and no side effects on breastfed infants of treated mothers have been shown. Approved for use as treatment on infants younger than a one year old. A low oral bioavailability would protect the infant, except in the neonatal period or cases of prematurity. Calcium contained in the milk prevents it from absorption by the gut. Be aware of the possibility of false negative results of bacterial cultures on febrile infants when the mother is on antibiotics.