Tox Tuesday: How drug-contaminated breast milk can harm infants

Infant health experts are increasingly extolling the benefits of breast milk for newborns and older babies alike, with many medical studies showing benefits that last long after infancy. Mothers are advised to breastfeed if possible, and human milk banks have sprung up to help deliver breast milk where enough isn’t naturally available.

Sadly, unhealthy substances can be transferred from mother to baby through breast milk. Take for example one Pennsylvania case in which a mother killed her 11-week-old child after breastfeeding him with a combination of methadone, amphetamine and methamphetamine in her system.

Even in cases where it’s not deadly, some substances can still harm a developing child. A recent study found that alcohol in breast milk may lead to lower cognitive abilities in kids.

How drugs get into human milk

Not all drugs work the same way in every breastfeeding person. How much of a substance actually reaches the milk depends on factors like its lipid solubility, molecule size and, most importantly, how much of a substance is in the mother’s bloodstream. That said, most drugs (prescription or otherwise) pass into human milk, and the more enters the blood, the more enters the milk.

Pediatrics expert Thomas Hale writes that the sooner it is after childbirth, generally, the more able drugs are to penetrate milk. Drugs pass from the blood through the capillary walls of alveolar cells lining the milk buds in the breast. Gaps allowing traces of drugs to enter the cells are closed when the alveolar cells swell, about a week after childbirth.

This is also why breastfeeding can pose new risks for the infant post-pregnancy — here, the infant has to metabolize a substance, but during pregnancy, the mother’s body metabolizes and eliminates drugs, Hale points out. Drugs taken 30–60 minutes before breastfeeding are most likely to be at peak blood levels during feeding, but this depends on the substance taken.

Other factors determining how much of a substance ends up in breast milk include ion trapping (when the low pH of human milk prevents drugs from returning into maternal circulation), high lipid solubility, protein binding, and lower molecular weight. How long the mother spends consuming the substance will also impact its levels in her bloodstream, as will the way a drug was administered (orally, intravenously, etc.).

Milk banks and other organizations that collect and distribute donated breast milk take strict measures to provide the safest nutrition possible. And this goes beyond drugs of abuse — even common over-the-counter medicines, coffee, nicotine, alcohol and other legal substances can impact a breastfeeding child. Neogen offers a validated panel of test kits for human milk testing, which can be used to ensure that a pool of milk is free of any risks to infant health.

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