Philadelphia ? Most children treated at major pediatric hospitals are given medicines not approved by the Food and Drug Administration for use in patients so young.

The study, in Tuesday’s Archives of Pediatrics & Adolescent Medicine, found that the sickest children and those undergoing surgery were most likely to get a so-called off-label drug. But altogether, nearly 80 percent of the children cared for at academic children’s hospitals got at least one medicine outside the age parameters approved by the FDA.

Researchers examined 90 commonly used drugs ranging from ibuprofen and morphine to dopamine and albuterol. Although their work was confined to hospitalized children, it comes just days after the FDA announced that it was reviewing the safety and effectiveness of over-the-counter cough and cold medicines in infants and toddlers.

“This issue of off-label drug use in children is a huge problem,” said Samir S. Shah, the study’s lead author and infectious-disease doctor at Children’s Hospital of Philadelphia.

The risk and benefits of many drugs in children are poorly studied, often because the drugmakers had little financial incentive to do so. While pediatricians differ on the scope and severity of the problem, the federal government is seeking more research.

One problem is that children and adults don’t metabolize drugs in the same way, said Donald Mattison, who heads a program at the National Institute for Child Health and Human Development that has identified nearly 50 medicines whose use in children most merits further study.

“I am constantly amazed with each of the drugs we study how different children are from adults,” Mattison said. “A lot of cases have left us scratching our heads.”

For example, morphine is an old pain drug, but pediatric experts alerted Mattison’s team that children treated with the drug had worse outcomes and more adverse events – such as bleeding into the brain – than those who did not get it.

Shah and his coauthors examined hospital records for 355,409 patients treated at 31 children’s hospitals in 2004 to identify those drugs most commonly used off-label and to determine the prevalence of the practice.

They defined off-label as drugs given to patients younger than the age established by the FDA.

“We don’t know whether in the absence of off-label use there would have been fewer deaths or more deaths,” Shah said. “I suspect that in many instances the drugs were beneficial and in a smaller number of cases the drugs were harmful.”

In 2002, Congress mandated that federal agencies identify those medicines whose use in children most merited further research.

“This list could and should help prioritize the drugs for further study,” Shah said.

Maureen Fee, chief medical officer of St. Christopher’s Hospital for Children in Philadelphia, said, “If you don’t do the studies, you can end up underdosing, overdosing, or using ineffective medicines.”

Still, Fee noted that the absence of labeling information did not necessarily mean a drug had not been well-studied.