Adverse effects of drugs and chemicals in breast milk on the nursing infant.

Breastfeeding is an essential physiologic process that provides nutrition to the infant and protects the child against infection and immunologic disorders. The incidence of various diseases and metabolic disorders is known to be less in a breastfed infant compared with a child given a milk substitute. Psychologically, a breastfed infant forms a maternal bond that enables adaptation more readily to a social environment. It is well-established that all drugs are excreted into breast milk and are bioavailable to the infant. In general the majority of drugs do not pose a significant problem to the nursing infant and breastfeeding should be encouraged. The physician should be aware of which drugs are contraindicated during lactation and which drugs should be used with caution. There are also environmental chemicals that readily enter breast milk and may induce adverse effects. At present, the advantages of breastfeeding for infant development outweigh the potential adverse consequences and this physiologic process should be encouraged. With the use of available data on pharmacokinetics, milk-to-plasma ratio, excretion, etc. a supportive approach can be delineated by the pediatrician to reassure the nursing mother that they can safely breastfeed and continue therapy with minimal effects on the infant. It is thus imperative to document the extent to which a drug or chemical appears in breast milk and any apparent effects in the infant.