Medications and Lactation: What PNPs Need to Know

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

J Pediatr Health Care. 2003;17(6)

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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Table. Drug information resources
Source	Contact Information
The Lactation Center	University of Rochester Medical Center 585-275-0088
Crozer-Chester Medical Center Drug Information Center	One Medical Center Boulevard Upland, PA 19013 610-447-2851
Brigham and Women's Hospital Boston, MA	617-732-5500; ask for clinical pharmacologist
Drugs in Lactation Web site (Hale)	www.neonatal.ttuhsc.edu/lact
Hale, T. W. (2002). Medications and Mother's Milk (10th ed.). Amarillo, TX: Pharmasoft	Ordering information: Pharmasoft Publishing Single copies $24.95, plus shipping 21 Tascocita Circle Amarillo, TX 79124-7301; tel: 800-378-1317; fax: 806-376-9901; www.iBreastfeeding.com
Drug Topics Red Book (106th ed.) (2002). Montvale, NJ: Medical Economics	Ordering information: www.medecbookstore.com
Briggs, G. G., Freeman, R. K., & Yaffe, S. J. (2002). Drugs in Pregnancy and Lactation (6th ed.)	Ordering information: Lippincott Williams & Wilkins, 530 Walnut Street Philadelphia, PA 19106

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