Morphine in breast milk

I read in the January issue of Canadian Family Physician about the tragic death of the baby resulting from the breastfeeding mother taking acetaminophen and codeine.1 “Following the development of poor neonatal feeding, the mother expressed milk and stored it in a freezer. Analysis of the milk for morphine … revealed a concentration of 87 ng/mL.… The morphine measurement was further confirmed by gas chromatography–mass spectrometry. “1

I have 2 questions.

Question 1: At 87 ng/mL, 1000 mL of breast milk would contain at total of 87 μg of morphine. How can such a small quantity be toxic to a baby that drinks only 60–90 mL at a time?

Also, “mass spectrometry revealed a blood concentration of morphine at 70 ng/mL and acetaminophen at 5.9 μg/mL. Neonates receiving morphine for analgesia have been reported to have serum concentrations of morphine at 10 to 12 ng/mL.” 1

Question 2: How can such small quantities of morphine in breast milk cause such high blood levels in the infant?

• Copyright© the College of Family Physicians of Canada