Breastfeeding is universally recognized as the preferred method of infant feeding and is associated with decreased infant mortality, but it is sometimes abbreviated because of fear of harm to the infant from maternal medication.¹ Despite this, physicians often receive little education on supporting breastfeeding. Comprehensive assessment can prevent unnecessary avoidance of breastfeeding, premature discontinuation of breastfeeding, or suboptimal treatment of the mother’s condition. This article provides information on the management of medications for common conditions during lactation.

Transfer of Medications Into Breast Milk

Medications enter breast milk through diffusion from serum, so milk concentrations depend on maternal serum drug concentrations and diffusion characteristics. Few medications are actively transported into breast milk.^2,3 Medications generally diffuse out of breast milk as the concentration in maternal plasma diminishes. Unlike the placental transport in pregnancy, medication absorption in breastfeeding is via the infant gastrointestinal tract.

The amount of medication that enters the infant through breast milk is determined by the medication concentration in the milk, volume consumed, and gastrointestinal absorption.^2,3 In the early postpartum period, large gaps between mammary alveolar cells allow medication to enter the milk more readily. This effect is mitigated by the small volume of colostrum consumed. Topical medications are generally safer than oral medications, although medications applied to the nipple may be concerning. The infant’s health can alter the effect of exposure to maternal medication. A smaller exposure may be significant in an infant with less ability to metabolize medications. The same medication exposure may be less problematic in an older, healthy infant who is nearly weaned.^2,3

Strategies to minimize infant exposure to maternal medication include dosing after breastfeeding and before the longest sleep interval for once-daily medications. Medications with poor oral absorption, low lipid solubility, and high protein binding are safest (Table 1²).

Breastfeeding Resources

Although pharmacologic knowledge can be helpful when prescribing medications for breastfeeding patients, use of up-to-date, accurate resources is essential. Table 2 lists resources for prescribing medications during lactation.^2,4–7 The LactMed database is produced by the National Library of Medicine.⁴ It is a comprehensive, authoritative resource that is peer reviewed, continuously updated, and available free online.

Several nongovernment resources are available. e-Lactancia originated in Spain and provides information in English and Spanish. It is produced by a nonprofit organization and includes similar information to LactMed but in a more user-friendly format.⁵ Thomas Hale’s Medications and Mothers’ Milk is a proprietary comprehensive resource available online, through a smartphone application, and as a textbook.² Drugs.com publishes patient information on medications in lactation and is regularly updated.⁶ MotherToBaby.org publishes patient-centered fact sheets on the use of many medications during lactation.⁷

The 2014 update of the pregnancy and lactation labeling rule from the U.S. Food and Drug Administration requires clearer labeling in package inserts about medication use during pregnancy and lactation; however, not all labeling has been updated.^8,9 A recent review of various resources for medication use during lactation found large variations, with package inserts being more restrictive and LactMed being the least restrictive.⁹

Specific Conditions

Table 3 summarizes prescribing guidance for common medical conditions while breastfeeding.^3,4,10–20