At least a quarter of outpatient antibiotic prescriptions filled in 2016 may have been unnecessary, researchers conclude in The BMJ.

Using a national U.S. claims database, the researchers identified over 15 million outpatient antibiotic prescriptions filled in 2016 by privately insured children and adults under age 65. The most common antibiotics used were azithromycin, amoxicillin, and amoxicillin-clavulanate, accounting for roughly half of prescriptions.

On the basis of ICD-10-CM diagnosis codes:

•  23% of prescriptions were classified as inappropriate, usually for acute bronchitis, acute upper respiratory tract infection, or respiratory symptoms.
• 36% were potentially appropriate, most frequently for acute sinusitis, acute suppurative otitis media, or acute pharyngitis.
• 13% were considered appropriate, most often for urinary tract infections, streptococcal pharyngitis or tonsillitis, and bacterial pneumonia.
• Some 29% of antibiotic prescriptions did not have an associated diagnosis code.