Breastfeeding mothers taking codeine aren’t harming babies: study

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Breastfeeding mothers who take codeine for post-childbirth pain aren’t putting their babies at a higher risk of danger, a large new Canadian study finds.

Many women were frightened off the painkiller several years ago after Toronto researchers reported the case of a healthy breastfed baby found dead when he was just 13 days old. His mother had been prescribed Tylenol 3 for postpartum pain. Lab tests showed high levels of morphine in her baby’s blood, even though she had been taking less than the recommended dose. Genetic tests revealed the woman was an ultrarapid metabolizer of codeine.

The liver converts codeine to morphine. Ultrarapid metabolizers turn codeine into morphine more efficiently than most. The authors concluded that the baby died from a morphine overdose and warned that morphine in breast milk might pose a danger to babies.

But Dr. David Juurlink, a scientist with the Institute for Clinical Evaluative Sciences in Toronto and lead author of the new study, said that even in women who convert codeine to morphine rapidly, “the amount of morphine present in breast milk is very, very small,” he said.

“Even if the baby was ingesting large amounts of breast milk, the amount of morphine they would ingest would be somewhere between 25 and 50 times lower than the newborn might actually be given to treat pain,” he said.

“It’s very difficult to argue convincingly that the amount of morphine that a child can ingest through breast milk is enough to be dangerous.”

His team looked at 7,804 babies born in Ontario between 1998 and 2008 whose mothers were prescribed codeine within seven days of delivery, and an equal number of babies whose mothers were not.

The babies were followed to see how many were readmitted to hospital for any reason within 30 days of life.

“We found that it didn’t seem to matter whether mum got a prescription for codeine or not,” said Juurlink, head of clinical pharmacology and toxicology at Sunnybrook Health Sciences Centre. There was no difference in the odds of readmission to hospital.

The researchers looked further: Were the babies of mothers prescribed codeine more likely to be hospitalized for resuscitation or dehydration? Were they more likely to be taken to hospital by ambulance? Were they more likely to die?

“The answer in each of those questions was, no, they were not,” Juurlink said.

Overall, 3.8 per cent of babies born to mothers who filled a prescription for codeine, and four per cent of infants whose mothers did not, were hospitalized for any reason within 30 days.

There are several important caveats: The researchers don’t know how many women were actually breastfeeding. “Breastfeeding is fairly common in Ontario and I think it’s safe to assume that a good number of women — especially in the first few weeks post-delivery — are going to at least try to breastfeed,” Juurlink said.

It’s also not known how many women prescribed codeine took the drug. The study involved women on social assistance who received at least one publicly funded prescription for codeine.

“Whether the results can be generalized to more affluent populations is not known,” the authors write in the current issue of the Journal of Clinical Toxicology.

They also didn’t look at the women’s genetic makeup.

Still, Juurlink says it is “extraordinarily unlikely” for codeine to be harmful to breastfeeding babies.

He stressed that the study is not meant to be an endorsement for using codeine “in anybody, nursing or otherwise.” Despite its widespread popularity, “codeine is simply not a rational drug,” Juurlink said.

“When a physician prescribes a known amount of codeine, what they’re really prescribing is an unknown amount of morphine, and that depends on the patient’s genetic makeup.”

An alternative would be to use an anti-inflammatory drug for pain, or morphine if the woman requires an opioid, he said.

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