Traditionally, codeine has been considered a safe analgesic for breastfeeding mothers.1 In the body, codeine is metabolized to morphine, but the amount of morphine excreted into the breast milk of most women was thought to be small.

Recently, the United States Food and Drug Administration (FDA) received new information about a potentially lethal side effect of codeine ingested by breastfeeding mothers who metabolize codeine differently than most of the population. As a result, the FDA issued a new public health advisory warning that the use of codeine by some breastfeeding mothers may lead to life-threatening side effects in their breastfeeding infants.2

The public health advisory was prompted by a report about a healthy 13-day-old breastfeeding infant who died of a morphine overdose. The infant's mother had been taking less than the usual dosage of codeine prescribed for postpartum episiotomy pain. Laboratory tests revealed high morphine levels in the infant's blood, and genetic testing proved that the infant's mother was an ultrarapid metabolizer of codeine.3

It is estimated that from 1 to 28 per 100 individuals are rapid metabolizers of codeine. It is impossible to know, without genetic testing, if a lactating woman's body changes codeine to morphine more rapidly and completely than does the average person, causing higher morphine levels in breast milk. Therefore, the FDA recommends that health professionals and nursing mothers be aware of and follow these safety guidelines:

* When prescribing codeine for a nursing mother, prescribe the lowest dose for the shortest amount of time to relieve pain. Physicians need to tell their nursing patients how to recognize signs of high morphine levels in themselves and their babies.

* The nursing mother taking codeine should be instructed to call her physician if she becomes extremely sleepy and has trouble caring for her baby.

* Breastfed babies usually nurse every 2 to 3 hours and should not sleep longer than 4 hours at a time. The nursing mother should be instructed that if her baby shows signs of increased sleepiness (more than usual), difficulty breastfeeding, to contact the baby's physician immediately, being certain to report what medications she is taking. If the baby shows signs of breathing difficulties or limpness, she should call 911.

For more information about the public health advisory, go to http://www.fda.gov/Cder/drug/advisory/codeine.htm.

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