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Member Research & Reports

Member Research & Reports

Northwestern: Measuring the Overuse of Outpatient Antibiotics

A new Northwestern Medicine study published in The BMJ provides the most extensive assessment of outpatient antibiotic prescriptions to date, and demonstrates the scale of inappropriate antibiotic prescribing in the U.S.

Using a novel classification scheme, the investigators determined that only 13 percent of outpatient antibiotic prescriptions were appropriate, with 36 percent considered potentially appropriate.

Dr. Jeffrey Linder, chief of general internal medicine and geriatrics and the Michael A. Gertz Professor of Medicine, was a co-author. Dr. Linder is also a member of the Institute for Public Health and Medicine at Northwestern.

The study is uniquely comprehensive: For the first time, the investigators evaluated all 91,738 diagnosis codes in ICD-10 (the system used in the U.S. to code diagnoses) and categorized each for antibiotic appropriateness. They also examined all outpatient antibiotic prescriptions among a cohort of 19.2 million patients, irrespective of the reason or site of care.

“Most prior studies have looked at antibiotic prescribing for a particular condition or in a particular location — for example, antibiotic prescribing for acute bronchitis in the emergency department,” Dr. Linder explained. “This allowed us to take a broader look at the appropriateness of antibiotic prescribing than has been done before.”

Overuse of antibiotics contributes to the development of antibiotic resistance — a major public health concern — increases healthcare costs, and exposes patients to unnecessary side effects.

Despite initiatives to curb the problem, a significant proportion of prescribed antibiotics are unnecessary. However, prior studies are limited in scope and largely out of date; in particular, most relied on diagnosis codes in ICD-9, although the system was replaced with ICD-10 in 2015.

In the current study, the investigators developed a new, comprehensive ICD-10-based classification scheme that determined whether each of the more than 90,000 diagnosis codes “always,” “sometimes,” or “never” justified treatment with antibiotics.

“No one had gone through all available codes before,” Dr. Linder said.

The team then used the new scheme to evaluate 15.5 million outpatient antibiotic prescriptions filled in 2016 by a large cohort of privately insured U.S. children and non-elderly adults. The investigators assigned each prescription fill to one of four categories: either “appropriate,” “potentially appropriate,” “inappropriate” or “not associated with a recent diagnosis code.”

They found that just 13 percent of prescriptions were appropriate, 36 percent were potentially appropriate and 23 percent were inappropriate. They also found that 28 percent were not associated with any diagnosis code at all — suggesting that the rate of inappropriate prescriptions may in fact be even higher.

“This means that our prior methods of looking at antibiotic prescribing based on location or specific diagnosis code is missing a huge proportion of antibiotics,” Dr. Linder explained.

Beyond highlighting the widespread overuse of antibiotics in the U.S., the study could also help facilitate future research; the authors note that the new classification scheme could be applied to any dataset using ICD-10 codes, providing a valuable tool for investigators.

Dr. Linder continues to lead large studies into the overuse of antibiotics. Most recently, Dr. Linder and collaborators at the University of Southern California launched a five-year study to examine antibiotic prescribing practices in telemedicine. The study is supported by the Health and Human Services Department’s Agency for Healthcare Research and Quality.

The BMJ study was supported by a grant from the Agency for Healthcare Research and Quality (R01HS024930), and a contract from the Agency for Healthcare Research and Quality (HHSP233201500020I).

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