Clinicians continue to treat resistant gram-negative infections with older, generic antibiotics that are considered to be less effective and less safe, even though FDA has approved seven next-generation gram-negative antibiotics between 2014 and 2019.

Researchers at NIH evaluated use patterns of recently approved gram-negative antibiotics and factors affecting clinicians’ preference for the newer drugs over traditional generic agents. After evaluating data from 619 U.S. hospitals, they found that 0.7% of gram-negative infection–related hospitalizations were difficult to treat resistant infections, and 41.5% of those infections were treated exclusively with older agents. These included “reserve” antibiotics such as polymyxins, aminoglycosides, and tigecycline in nearly 80% of the episodes, according to the findings, which were published in the Annals of Internal Medicine.

The most frequently used next-generation antibiotics between January 2016 and June 2021 were ceftolozane-tazobactam and ceftazidime-avibactum, while other more recently approved antibiotics had a more “sluggish” uptake, the researchers noted.

Patients who had higher adjusted probabilities of receiving newer verses traditional antibiotics for difficult-to-treat resistant infections include those with bacteremia and chronic diseases. Meanwhile, patients with do-not-resuscitate status, acute liver failure, and Acinetobacter baumannii complex and other nonpseudomonal nonfermenter pathogens had lower adjusted probabilities of being treated with newer antibiotics.

“Future antibiotics with innovative mechanisms targeting untapped pathogen niches, widely available susceptibility testing, and evidence demonstrating improved outcomes in resistant infections might enhance utilization,” the researchers wrote.