Earlier this year, a study showed that nearly one-in-three antibiotics prescriptions in the U.S. aren’t necessary, and a new analysis of available medical data claims that only half of the people who receive antibiotics for the most common types of infection are receiving the right kind of drug.

This is according to the latest joint report from the Pew Charitable Trusts and the Centers for Disease Control and Prevention, which looked at prescribing data from the National Ambulatory Medical Care Survey to see which drugs were being prescribed to patients with middle ear infections, sinusitis, and pharyngitis.

Why those three conditions? Because they are incredibly common, resulting in about 44 million — or 1/3 of all — antibiotics prescriptions written each year.

Ideally, these conditions should be treated with narrow-spectrum antibiotics like Amoxicillin-clavulanate or Amoxicillin-penicillin. These “first-line” drugs may actually be more effective than the broad-spectrum alternatives, and there are also lower risks of side effects, including diarrhea-inducing Clostridium difficile infections that can result from going the broad-spectrum route. Additionally, overuse of broad-spectrum drugs that are used to treat multiple types of bacteria can encourage antibiotic-resistant pathogens. Drug-resistant diseases afflict more than two million Americans every year, according to the CDC, killing more than 20,000.

Yet, this new report found that — particularly in adults — doctors are frequently prescribing broad-spectrum drugs when they are not needed or may be less effective.

For example, only 37% of adult sinusitis or pharyngitis patients received recommended first-line antibiotics. Macrolides — a class of antibiotics that includes azithromycin — were the most frequently prescribed drugs for these patients. However, Pew points out that these broad-spectrum antibiotics are not recommended for sinus infections and are only recommended for pharyngitis when the patient has an allergy to the penicillin class of antibiotics.

Children are much more likely than adults to get proper first-line antibiotics, according to this analysis. For all three conditions, the majority of pediatric patients received the recommended medication, with 60% of pediatric pharyngitis patients getting prescriptions for the correct first-line treatment.

Yet even those numbers are far below the levels recommended by the panel of experts put together for the Pew report. Acknowledging that not every patient can be treated with the narrow-spectrum first-line drugs — as much as 10% of the population may be allergic to penicillin — they contend that 80% of these prescriptions should be for the recommended first-line antibiotics.

“This study provides evidence of substantial overuse of non–first-line antibiotics for three of the most common conditions in ambulatory care,” concludes the study, which was published today in JAMA Internal Medicine. “These findings indicate that the problem of inappropriate antibiotic prescribing includes not only prescriptions that are unnecessary altogether, but also selection of inappropriate agents. As a result, stewardship interventions should address both antibiotic overuse and inappropriate antibiotic selection to improve patient safety and health care quality.”

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