Nursing mothers taking codeine should watch their infants for increased sleepiness or other signs of overdose, U.S. federal health officials warned Friday.

The Food and Drug Administration (FDA) warning of the rare but serious side-effect was prompted by a 2006 report of the death of a nursing infant whose mother was given codeine for pain following an episiotomy.

Codeine is included in several prescription pain drugs and in some over-the-counter cough syrups.
(CBC)

Tests revealed the woman's body converted the codeine to morphine more quickly than in other people due to a genetic mutation. The rapid conversion led to higher-than-expected morphine levels in her breast milk.

The risk of having the genetic mutation ranges from about one per cent in Hispanics, Chinese and Japanese, to three per cent in African-Americans, one per cent to 10 per cent in Caucasians, and as high as 16 per cent to 28 per cent in North Africans, Ethiopians and Saudis, said Sandra Kweder, the FDA's deputy director, office of new drugs, Center for Drug Evaluation and Research, in a release.

While the rapid conversion of codeine to morphine is a very rare side-effect in some mothers, it can result in high and unsafe levels of morphine in the blood and breast milk, said the FDA.

Close monitoring required

Codeine is among the most common drugs taken by new mothers, FDA officials said. It is included in several prescription pain drugs and in some over-the-counter cough syrups. 

According to Health Canada's drug product database, some of these include:

• Tylenol No. 1 caplets, Tylenol with Codeine No. 2 and Tylenol No. 3
• 222
• Dimetapp C Syrup
• Robitussin A-C Syrup
• Sinutab with codeine

Given the risk, doctors should prescribe nursing mothers the smallest dose of codeine for the shortest period of time, the FDA recommended. Doctors also should closely monitor both mother and child.

Signs of morphine overdose in children, beyond increased sleepiness, include difficulty breast-feeding or breathing and limpness. Nursing mothers may also experience overdose symptoms, such as extreme sleepiness, confusion, shallow breathing or severe constipation, the FDA said.

New mothers taking codeine who find themselves extremely sleepy should consult their doctor. If their baby seems unusually sleepy or has trouble nursing they should contact their physician or take the baby to an emergency room, said Kweder.