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

Breast Milk pH

The average plasma pH is 7.4, and the mean pH of breast milk is lower at 7.2 (Begg, Duffull, Hackett, & Ilett, 2002). Drugs that are weakly basic (i.e., more alkaline) tend to concentrate to a greater extent in the more weakly acidic breast milk, as opposed to the less weakly acidic plasma since acids attract bases (Auerbach & Riordan, 1998). Furthermore, weak bases are nonionized in the maternal plasma. This increases their ability to be transferred into breast milk, and thus, they may have a greater potential to become ion-trapped in the breast milk. Conversely, drugs that are weak acids are ionized in maternal plasma, which minimizes their diffusion into breast milk. For example, antihistamines and erythromycin, drugs that are weakly basic, would be more likely to cross cell membranes from maternal plasma into breast milk than would penicillins, which are weakly acidic (Banta-Wright, 1997).


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