As health experts battle deadly and seemingly immortal bacteria, a new study shows that hospitals are not doing nearly enough to support antibiotic stewardship.

A new study by researchers with the U.S. Centers for Disease Control and Prevention (CDC) shows just how often some hospital patients are given multiple antibiotics.

According to the study, published in the Journal of the American Medical Association, half of all hospitalized patients receive at least one antimicrobial drug on a given day, most for treating a variety of infections. Half of those patients receive more than one antimicrobial drug, and more than 5 percent take four or more antimicrobial drugs.

The most surprising finding was that of the 83 different antimicrobial drugs used, just four accounted for 45 percent of the treatments. The drugs were most commonly used in patients with hospital-acquired infections and in critical care settings, but also for patients with less serious infections.

Up to 23 percent of the recorded antibiotic use was for infection prevention or had no documented purpose, the study showed.

This is a serious concern for experts because the inappropriate use of antibiotics is tied to more serious drug-resistant infections, as well as adverse drug events. This continued practice — broadly administering important antibiotics — gives bacteria ample opportunity to develop defenses against the drugs.

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“To minimize patient harm and preserve effectiveness, it is imperative to critically examine and improve the ways in which antimicrobial drugs are used,” the researchers wrote. “Improving antimicrobial use in hospitals benefits individual patients and also contributes to reducing antimicrobial resistance nationally.”

The CDC researchers stated that if hospitals focused on the four most-used drugs and on reducing the three most common types of infection — lower respiratory tract, urinary tract, and skin and soft tissue infections — they could address more than half of all inpatient antibiotic use.

The CDC researchers reached their conclusions by using data from 11,282 patients in a one-day snapshot of 183 acute care hospitals in 10 states.