to the editor: The article about medications and the breastfeeding mother mentions the paucity of data regarding the use of medications by lactating women.¹ The U.S. Food and Drug Administration (FDA) has participated in numerous workshops and conferences with other government agencies (National Institutes of Health [NIH], National Institute of Child Health and Human Development [NICHD], Centers for Disease Control and Prevention [CDC]), academia, and the pharmaceutical industry to raise awareness on this issue.

Obstacles to conducting studies in lactating women include limited funding, ethical considerations, legal issues, and safety concerns; however, these obstacles are not insurmountable. Giving patients and physicians only the option of either “pumping and dumping” or stopping breastfeeding is unacceptable for either group.

Systemic exposure to a drug in the nursing infant is related to the concentration of the drug in breast milk and the amount of breast milk consumed. However, other factors that play an important role in the infant's exposure to drugs² include the location of drug absorption in the gastrointestinal tract, local effects on the gastrointestinal flora, and the infant's renal and hepatic capacity, which vary and mature with age.^3,4 Caution should be exercised with the recommendation that if the drug is safe for the infant, it can be safely taken by the lactating mother. The dose received via breast milk also reflects the maternal dose, which is usually several orders of magnitude greater than a therapeutic infant dose.

The authors indicate that the information in the Physicians' Desk Reference (PDR) is often inaccurate.¹ Pharmaceutical companies pay a fee to the publisher to have product information included in the PDR. Further, new information about marketed drugs may not be included in labeling information. After a drug is marketed in the United States, new data can be incorporated into the label only if the pharmaceutical company that owns that drug submits the data along with the labeling supplement for FDA review and approval.⁵ Most published data regarding drugs and lactation are not proposed by companies to be included in drug labels, and there is no requirement that they do so. The FDA, through several scientific and regulatory initiatives, is working to change this and facilitate rational prescribing for pregnant and lactating women.

in reply: We appreciate the comments of the authors from the U.S. Food and Drug Administration (FDA) regarding our article. A specific example may clarify our comments regarding the quantity of drug present in breast milk following a maternal dose.

After a 1-g dose of amoxicillin, breast milk levels peak at 1.3 mg per L.¹ The average breastfed child ingests 800 g of milk per day.² This would result in the ingestion of 1 mg of amoxicillin from the milk (assuming the peak concentration were maintained throughout the day, which is generally not the case). This dose is far less than the usual pediatric therapeutic dose of 40 mg per kg per day. The possibility does exist that this small dose could cause an allergic reaction or alterations in the child's gut flora. Nevertheless, we conclude that, for this example, the drug exposure to the breastfed infant following maternal use is unlikely to be clinically important.

We wish to emphasize that this rationale is most useful for medications that can be used directly for the breastfeeding child.