Breastfeeding & Drugs: Does the medication pass into the breast milk?

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Breastfeeding and Drugs Topics
Table of Contents
Pre module evaluation
Prescription and Over the Counter Medications
Case Study 28
Case Study 29
Pain Medications
Illicit Drugs
Post module evaluation

  1. The epithelium of the breast milk alveolar cells is most permeable to drugs during the first week post-partum, so drug transfer to milk may be greater during the first week of an infant's life.

  2. Drug excretion into the milk depends on a number of factors related to the drug including ( Memorize Lawrence, 2011 p. 365-369):

    1. Ionization of the drug - Drugs that are not protein bound and nonionized are more likely to be transferred into breast milk.

    2. Molecular weight of the drug - Lower molecular weight drugs are more likely to be transferred to the breast milk than higher molecular weight drugs.

    3. Solubility of the drug in lipids and waters - Lipid soluble drugs pass more freely into breast milk than water soluble drugs.

    4. The pH of the plasma and the milk - Weakly alkaline drugs have higher breast milk levels than weak acids.

  3. Once the drugs have reached the alveolar cells of the breast they may then be transferred into the milk by:

    1. Diffusion: the movement of the drug from a high concentration area (blood) to a low concentration area (breast milk).

    2. Active transport: the movement of the drug from blood with a low concentration to breast milk with a high concentration. This mechanism concentrates the drug in the breast milk.

    After diffusion or active transport, drugs pass through spaces between alveolar cells into the milk ( Memorize Lawrence, 2011 p. 369).

  4. Most ingested drugs that appear in the milk do not exceed 2% of the ingested dose and the binding of the drug to milk proteins is less than the binding to plasma proteins ( Memorize Powers, 1997 ).

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