Medications and Lactation: What PNPs Need to Know

Jennifer M. Marks, BS; Diane L. Spatz, PhD, RNC


J Pediatr Health Care. 2003;17(6) 

In This Article

Lipid Solubility of the Drug and Fat Content of Milk

Lipid-soluble drugs readily diffuse across cell membranes by dissolving in the lipid bilayer. Almost without exception, a medication that is more lipid-soluble will transfer more quickly, and in greater amounts,into breast milk than one that is less lipid-soluble (Riordan & Auerbach, 1998). Water-soluble drugs must pass through pores to cross cell membranes, a process that slows diffusion. Since medications with low lipid solubility and those that are water-soluble diffuse slowly into breast milk, they are preferred for use in breastfeeding mothers (Banta-Wright, 1997).

Colostrum is low in lactose and fat and high in protein. The reverse is true of mature milk. Because mature milk has a higher fat content than colostrum, a lipid-soluble drug given during the late postpartal period will appear in breast milk at a higher levelthan if it had been given in the early postpartal period (Auerbach, 1999). However, even mature milk has a low proportion of fat to total milk volume and probably allows only a small amount of a medication to reach the infant (Banta-Wright, 1997).


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