Doctors should think twice before giving young children codeine, and the popular painkiller should never be prescribed after the most common tonsillectomies, Canada's top pediatric drug expert says.

In a letter published today in the New England Journal of Medicine, Dr. Gideon Koren calls for an end to the routine practice of giving toddlers codeine after tonsillectomies aimed at curing sleep apnea, which he says could kill some children.

Moreover, the founder of the Hospital for Sick Children's Motherisk program says the drug may have dangerous side effects on many children and doctors should consider alternate analgesics after operations on the very young.

"Even if North America uses codeine ... as a gospel, we may need to rethink our way of treating people," says Koren, specifically about children 5 years and younger.

With effective alternate pain relievers available, Koren says, codeine medications should be avoided in toddlers, or only be prescribed at the lowest recommended doses for post-operative pain relief.

Several thousand Canadian children undergo tonsillectomies each year, the vast majority to relieve sleep apneas.

The journal warning was based on a study that looked at the death of a 2-year-old boy who was given codeine after a tonsillectomy. He died days later of respiratory complications the drug might have caused.

Though it is unusual to tie so sweeping a recommendation to a solitary case, Koren says he had no qualms about issuing the prestigious journal alert.

"It's the first child we could prove that died (from potential codeine complications) ... but other kids die after tonsillectomy and often times the reason is not known."

Codeine, an opiate, is metabolized by the body into morphine, a potent painkiller and known respiratory suppressor.

But some people are genetically programmed to metabolize it much more rapidly than others, leaving them with higher concentrations of morphine in their systems.

In 2007, the U.S. Food and Drug Administration issued a similar warning for new mothers, saying they would undoubtedly be "ultra-rapid" metabolizers of the drug and risked feeding their babies high levels of morphine through breast milk.