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Am Fam Physician. 2022;106(6):638-644

This clinical content conforms to AAFP criteria for CME.

Author disclosure: No relevant financial relationships.

Breastfeeding is universally recognized as the preferred method of infant nutrition, but is sometimes abbreviated because of fear of harm to the infant from maternal medication. The amount of medication that enters breast milk varies based on the maternal serum concentration and the pharmacologic properties of the medication. When prescribing medications for a breastfeeding patient, those with the lowest risk to the infant should be selected, and dosing should be before the infant’s longest sleep interval. Prescribers should use current, accurate resources. LactMed is a convenient, government-sponsored, authoritative resource that lists safety information for many medications and is available free online. When mental health conditions occur during lactation, priority should be given to effectively treating the mother, often with medications that were effective during pregnancy. Most antidepressants are compatible with breastfeeding. Stimulant medications may decrease milk supply. Insulin, metformin, and second-generation sulfonylureas are generally preferred to treat diabetes mellitus during breastfeeding, but newer agents require caution because they have not been studied in lactation. Inhaled and nasal treatments for asthma and allergic rhinitis are unlikely to affect breastfed infants. Acetaminophen and ibuprofen are preferred analgesics during lactation. Maternal opioid use can cause infant sedation. Herbal supplements are concerning for risk of impurities and lack of study of effects on breastfed infants. Nonhormonal and progestin-only contraceptives are preferred over combination oral contraceptives. Contrast for computed tomography or magnetic resonance imaging is not concerning during lactation, but use of radiopharmaceuticals, such as iodine 131, can accumulate in the lactating breast and increase risk to the infant.

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).

General considerations
Avoid drug therapy when possible.
Medications that are safe for use in an infant are generally safe for the breastfeeding patient.
Medications that are safe in pregnancy are not always safe while breastfeeding.
Use reliable references for obtaining information on medications in breast milk.
Use topical therapy when possible (except on the nipple).
Medication selection
Choose medications that are well studied in infants.
Choose medications with the lowest lipid solubility, poorest oral absorption, shortest half-life, and highest protein-binding ability.
Medication dosing
Administer single daily-dose medications just before the longest sleep interval for the infant, usually after the bedtime feeding.
Breastfeed infant immediately before medication dose when multiple daily doses are needed.

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.2,47 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.

For prescribers
 Free, peer reviewed, authoritative, and regularly updated e-Lactancia
 Free, available in English and Spanish, peer reviewed, and regularly updated
Medications and Mothers’ Milk
 Authoritative textbook written by Thomas Hale, website and smartphone application require a subscription
For patients
Free general pharmaceutical database, includes well researched lactation information
 Free information on medications in pregnancy and lactation, available in English and Spanish

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 publishes patient information on medications in lactation and is regularly updated.6 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.3,4,1020

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