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Pediatricians write more than 10 million unnecessary antibiotic prescriptions—for conditions like the flu and asthma—every year, suggests a new study.

Those ailments, and others not caused by bacteria, don't respond to the drugs. But misuse of antibiotics contributes to drug resistance—so those same medications might not work in the future when they're really needed.

"Antibiotics are wonderful. There are times you really need them, the question is just being judicious about when we use them," said Betsy Foxman, an epidemiologist at the University of Michigan School of Public Health in Ann Arbor who was not involved in the research.

The new study involved a nationally-representative sample of almost 65,000 outpatient visits by kids under 18 in 2006 through 2008. Using medical codes, researchers were able to determine the type of diagnosis kids were given, as well as what kind of drugs, if any, they were prescribed.

In total, doctors prescribed an antibiotic at one in every five visits. Most prescriptions were given out for kids with respiratory ailments, including sinus infections and pneumonia.

Some of those infections are caused by bacteria, and antibiotics are warranted. But almost one-quarter of all antibiotic prescriptions were given to kids with respiratory conditions that probably or definitely do not call for antibiotics—such as bronchitis, the flu, asthma and allergies.

That translates to more than 10 million antibiotic prescriptions each year that likely won't do any good but might do harm, Dr. Adam Hersh of the University of Utah in Salt Lake City and his colleagues reported today in Pediatrics.

Half of all antibiotics prescribed were "broad-spectrum" drugs—meaning they act against a wide range of bacteria. Those "kill more of the good bacteria in our bodies and can set the child up for infections with antibiotic resistant bacteria down the road," Hersh wrote in an email to Reuters Health.

"In many of these instances antibiotics are not indicated at all," he added.

Broad-spectrum antibiotics include macrolides and certain types of cephalosporins and penicillins.

Foxman said that wiping out the non-harmful bacteria in the intestines has been linked to asthma and, recently, to obesity.

"We think of antibiotics as being wholly beneficial, but they are not very specific, they hit everything in your body," she said. "By making our microbes that are supposed to be with us disappear, we can be causing other health problems we don't know about."

And even when the drugs are prescribed for just a few days, giving them to lots of kids unnecessarily raises the risk of antibiotic-resistant infections in the kids themselves, and for society as a whole, she added.

"It's been known for a very long time... that people are prescribing antibiotics for upper respiratory infections where they have no benefit," Foxman told Reuters Health.

"To me this wasn't a big surprise, though it's certainly disturbing."

Hersh said that there are a number of reasons why doctors might prescribe antibiotics when they're not likely to help. "One reason overuse occurs is because the diagnosis is often unclear—this is common with ear infections. The decision is made to prescribe an antibiotic even though the diagnosis isn't certain, just 'to be on the safe side,'" he said.

In those cases, a "wait and see" approach in which the kid comes back to the office a couple days later might avoid an unnecessary prescription, he added.

"If your doctor suggests an antibiotic prescription, for instance for an ear infection, ask how certain the diagnosis is. If the diagnosis is still a little unclear, ask if it would be safe to wait a day or two with close follow up rather than starting the antibiotic right away," Hersh advised.

Dr. Aditya Gaur, who has studied antibiotic prescribing at St. Jude Children's Research Hospital in Memphis, said that parents should ask doctors why their kids are getting whatever particular medication, including antibiotics, they're being prescribed.

"Parents and families should be part of the decision and ask why (something) is being done," Gaur, who wasn't linked to the study, told Reuters Health. They should also know "not to expect an antibiotic every time an infection is diagnosed."