Most drugs have been found to be excreted in human breast milk. Usually when the drug is taken in therapeutic amounts for short periods of time by the mother, the levels of the drug in breast milk are sufficiently low to be of little hazard to the infant. However, is a breast-feeding infant should become ill or fail to thrive and the morbidity cannot be explained, one of the following should be done: 1. Discontinue the drug. 2. Discontinue breast feeding. Frequently this can be accomplished on a temporary basis with the mother pumping her breasts to maintain lactation while the response of the infant is monitored. 3. Collect maternal plasma, breast milk, and infant plasma samples for drug assay. In situations in which this can be accomplished, it may be possible to incriminate (or exonerate) a drug or one of its metabolites as the source of the morbidity on the basis of the amounts of drug found in the milk or the infant's plasma. As tedious and impractical as this approach may seem, it would eventually lead to the accumulation of a reasonable amount of data from which could be drawn sensible conclusions about the effect of drugs on the breast-fed infant.
PIP: The increasing prevalence of breastfeeding along with the frequency of pregnancies in females with chronic medical conditions have increased the number of patients who face possible harmful effects on the newborn of medication excreted in breast milk. Guidelines are provided for patients and practitioners in order to make reasonable judgments in these situations. Mothers who are nursing should not be given medications unless there is convincing evidence that the drug will benefit the condition for which it is being prescribed. Deterioration of the mother's health in either an acute or chronic illness will prove more detrimental to breastfeeding than will the effect of most medical treatments of her condition. The pharamcokinetics of most drugs ingested by breastfeeding women are such that administration of the drug at or immediately following the infant nurses will result in the lowest amount of drug in the milk at the subsequent feeding. The amount of a drug or its metabolite that enters the breast milk is dependent upon the extent to which the substance is ionized, lipid soluble, and bound to plasma proteins. Generally, drugs known to be extensively protein bound are excreted in breast milk to a lesser extent than drugs that are poorly bound to plasma proteins. Drugs that may have an adverse effect on lactation include oral contraceptive steroids, ergot derivatives, and pyridoxine (vitamin B6). Drugs that may have an adverse effect when ingested by a breastfed infant include cyclophosphamide, chloramphenicol, metronidazole, nitrofurantoin, antithyroid drugs, psychotropic drugs, and radiopharmaceuticals.