Relatively few clinical trials have tested the safety and effectiveness of medications in children - even when kids make up a large share of patients with the condition the drug treats, a new study finds.
That most clinical drug trials do not include children and teenagers has long been known. It has meant that many medications on the market are not specifically approved for kids.
And in practice, doctors often have to "extrapolate" findings from adult studies and try to apply them to children - giving kids a lower dose of a drug that's been found effective in adults, for instance.
But children are not small adults, Dr. Florence T. Bourgeois, lead researcher on the new study, pointed out.
They metabolize drugs differently than adults do, and their developing bodies may respond differently.
But historically, it has been hard to get pediatric clinical trials done. One issue is the ethics of giving untested drugs to children, explained Bourgeois, an assistant professor at Harvard Medical School and Children's Hospital Boston.
"It may simply be hard to recruit children," she said. "Both parents and doctors may be hesitant to include them in trials."
Then there are the market forces. Drug companies do not have much incentive to do pediatric trials because most diseases are uncommon in children.
For the new study, Bourgeois and her colleagues looked at more than 2,400 clinical trials conducted between 2006 and 2011. The trials all focused on conditions for which children make up a large share of patients.
In wealthy countries, that meant asthma, migraines, schizophrenia, bipolar disorder and depression. In lower-income countries, it was conditions like malaria, diarrhea and lung infections.
Overall, just 12 percent of the trials focused on children and teenagers. Yet kids accounted for 60 percent of those suffering the conditions studied.
"Children continue to be underrepresented in clinical trials compared with their burden of disease," Bourgeois said.
And that, she noted, is despite legislation passed in recent years and designed to encourage more pediatric trials.
In the U.S., drug companies can extend their marketing rights for a drug if, by request of the Food and Drug Administration (FDA), they study its effects in children.
The FDA also has the authority to require pediatric studies of certain medications.
"I think the concern is that this legislation may not be sufficient," Bourgeois said.
FDA declined to comment on the new findings, saying the agency needed more time to review the research.
But an FDA spokesperson said progress is being made in pediatric drug research.
"One of FDA's top priorities is giving pediatricians and parents the same level of tested and researched information on drugs used to treat children that is required for drugs used to treat adults," Sandy Walsh said in an email.
"Congress has helped increase studies for children by passing legislation that gives companies financial incentives to conduct pediatric studies and to require them to study a product they are developing for adults if the disease also occurs in children," Walsh added.
Bourgeois said that more may need to be done to encourage not only drug company trials, but studies funded by non-commercial sources as well.
Of the research included in this study, pediatric trials were more likely to have been funded by government or non-profits: 59 percent of them were, versus 35 percent of adult trials.
Dr. Kenneth D. Mandl, an associate professor at Harvard who also worked on the new study, said there is a need as well for studies that go beyond the initial clinical trial.
When kids have chronic health conditions, it could mean they will be using a medication for years or even decades. And the possible effects on their development and overall health are not known.
So studies that follow patients in the "real world" are needed, Mandl said, to try to identify any unanticipated adverse effects in the long term.
Despite all the questions, though, Bourgeois said the intention is not to scare parents away from letting their children have needed medications, such as asthma drugs.
She said that if parents have concerns, they can ask their pediatrician questions - including how often they prescribe the medication, and whether they know of any adverse effects associated with it.