Safety during breastfeeding: drugs, foods, environmental chemicals, and maternal infections.

The two ultimate goals of using maternal medications during breastfeeding are (i) to provide definitive therapy for maternal conditions for which the drugs have been prescribed, and (ii) to assure protection of the nursing infant from any adverse event related to his/her mother's treatment. Fortunately there are only a few drugs that have been identified as potentially causing harm to the infant. Analytic techniques exist to measure compounds in concentrations as small as nanograms per liter of milk. For nearly all compounds these very small amounts would not be able to exert pharmacological activity, even if absorbed by the infant via the oral route. For environmental chemicals, this ability to measure very small amounts exceeds our knowledge of any biological activity. Concern over any possible adverse event to the nursing infant should take into account the drug, its dose, the age of the infant, recognition of the interindividual variation in drug response and the role of pharmacogenetics. The latter two variables are closely linked.