Nearly a fourth of outpatient antibiotics unneeded, study finds

New data published yesterday in the British Medical Journal indicate that nearly a quarter of all US outpatient antibiotic prescriptions filled by adults and children with private insurance in 2016 were unnecessary, with 1 in 7 filling at least one inappropriate prescription for an antibiotic.

But the authors of the study say the true number of inappropriate antibiotics doled out that year is likely much higher.

The study, conducted by researchers from the University of Michigan Medical School, Brigham and Women's Hospital, and Northwestern University Feinberg School of Medicine, looked at antibiotic prescriptions and associated diagnostic codes for more than 19 million patients with private health insurance and found that 13% of those prescriptions were appropriate and 23% were inappropriate. But the rest were either labelled as "potentially appropriate" or were not associated with a recent diagnostic code—two categories that could also contain many unnecessary antibiotic prescriptions.

Defining inappropriate prescribing

The study is noteworthy for its novel methodology. The researchers went through more than 91,000 ICD-10 diagnostic codes to come up with a classification scheme to assess the appropriateness of all outpatient antibiotic prescriptions recorded in a national insurance claims database.

The scheme grouped the diagnostic codes according to whether the associated indications always, sometimes, or never justified antibiotics, and those labels were then used to determine which antibiotic prescriptions were appropriate, inappropriate, or potentially appropriate. An additional category was for prescriptions that weren't associated with any recent diagnostic code.

Previous outpatient prescribing studies, most notably a widely-cited 2016 JAMA study that estimated roughly 30% of all outpatient antibiotics prescribed in doctor's offices and emergency rooms are unnecessary, have used pre-2015 data and ICD-9 codes. This is the first study to use ICD-10 codes, which went into effect in October 2015.

In addition, while the study was limited to privately insured patients, it had a wider scope than previous studies, which have focused on outpatient antibiotic prescribing for select conditions (like upper respiratory tract infections) or in certain outpatient settings. "Our claims data are able to look at prescribing across a greater number of settings, but we were also able to conduct patient-level analyses, because claims data are essentially a record of all the utilization and diagnoses and claims that a particular patient accumulates," lead study author Kao-Ping Chua, MD, PhD, a pediatrician and professor of pediatrics at the University of Michigan Medical School, told CIDRAP News.

Using this method, Chua and his colleagues evaluated 15.4 million antibiotic prescriptions filled in 2016 by 19.2 million patients between the ages of 0 and 64 years enrolled in private insurance—a rate of 805 antibiotics prescriptions per 1,000 enrollees. They found that 12.8% of the prescriptions were appropriate, 23.2% were inappropriate, 35.3% were potentially appropriate, and 28.5% were not associated with a recent diagnostic code. The diagnostic codes most frequently attached to inappropriate prescriptions were acute bronchitis, acute upper respiratory tract infection, and respiratory infections such as cough.

Chua said that while the 23.2% of prescriptions found to be inappropriate is concerning, that number by itself doesn't tell the entire story.

"You can be sure about the 13% of appropriate prescriptions that were associated with diagnoses like urinary tract infections and pneumonia…and then for the other 87%, you're not so sure about," he said.

The potentially appropriate category includes conditions like sinusitis and pharyngitis, primarily viral infections that are commonly—and often unnecessarily—treated with antibiotics. "Much of sinusitis is viral, and yet we know that the vast majority of people who have that diagnosis will get antibiotics," Chua said.

But Chua and his colleagues labelled those diagnoses as potentially appropriate to account for cases where the infections were actually caused by bacteria, or where the coding wasn't accurate. Likewise, some of the prescriptions not linked with a diagnostic code—what Chua calls the "phantom" category—could be legitimate. They may have been refills for appropriate antibiotics, or were obtained at an urgent care or retail clinic and weren't covered by insurance. But they could also be inappropriate prescriptions that were obtained over the phone or online, with no patient examination to determine if they were necessary.

"In all the decisions we made, we kind of tried to lean toward the side of giving people the benefit of the doubt, and even despite that, you still get these alarming percentages," Chua said.

Providers pushed toward prescribing

On a population level, the analysis found that 14.1% of the 19.2 million patients—or 1 in 7—filled at least one inappropriate prescription in 2016, translating to more than 2.6 million patients. A sub-group analysis by age showed that 15.2% of adults filled at least one inappropriate prescription, compared with 10.6% of children.

Although he cautioned that the study population is not nationally representative, those are the numbers that jump out at Chua.

"Given that there are 320 million Americans in the country, 1 in 7 ends up being a very large number," he said. "That kind of population-level estimate, as opposed to the prescription-level estimate, is in some sense more effective at illustrating the scope of inappropriate antibiotic use, how common it really is, and how much progress we need to make."

Chua said that while the issue of overprescribing is complicated, it ultimately boils down to a central dynamic that nudges physicians toward prescribing an antibiotic, even when the diagnosis is uncertain. Patients come in with an illness and expect treatment, providers want to help but don't have a lot of time to explain why antibiotics aren't necessary for their illness, and concerns about adverse effects and antibiotic resistance aren't enough to dissuade patients from using antibiotics.

In addition, providers aren't penalized for overtreating patients.

"There are a lot of things that push us toward prescribing, and it's hard to change," Chua said. But he does think that there are strategies that can change the dynamic, including increased patient education and provider-focused interventions that steer physicians away from unnecessary prescribing.   

"We have to do something, because if we don't, then the superbugs that are already here are going to continue to proliferate, and we just don't have enough antibiotics in the pipeline," he said.

Chua and his co-authors also say they think the methodology they developed for the study can be used to get a better sense of outpatient antibiotic overuse in the United States and other countries that use ICD-10 codes. "Our scheme could be a valuable tool for policymakers and researchers interested in measuring and improving the appropriateness of outpatient antibiotic prescribing," they write.

See also:

Jan 16 Br Med J study

May 4, 2016, CIDRAP News story "Study: 30% of outpatient antibiotic prescriptions unnecessary"

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