In vitro Activity of Cefmetazole and Flomoxef among Extended-Spectrum Beta-Lactamase producing Enterobacterales.

In this age of antimicrobial resistance (AMR), improving treatment using existing antibiotics is desirable. Extended-spectrum beta-lactamase (ESBL)-producing Enterobacterales (ESBL-E) are high priority AMR pathogens according to the World Health Organization. Cephamycin-class beta- lactams are tolerant to hydrolysis by ESBL activity and have bactericidal effects on ESBL-E. The aim of the present study was to compare the in vitro minimum inhibitory concentration (MIC) of cefmetazole (CMZ) and flomoxef (FMOX) among ESBL-E strains. This was a retrospective study using microbiology laboratory data from Okayama University Hospital (Japan) from January 2014 to June 2022. The MIC was determined by broth microdilution method and the ESBL phenotypes were determined by double-disk method. Antimicrobial use density (AUD) data for CMZ and FMOX were also gathered. Annual proportions of ESBL-producing organisms in Escherichia coli, Klebsiella pneumoniae, and Enterobacter cloacae complex were 20.4-30.6%, 3.5-13.7%, and 0-3.1%, respectively. The ESBL-producing bacteria with MIC levels ≤1 μg/mL for CMZ and FMOX ranged from 57 to 84% and 97 to 100%, respectively, for E. coli, and from 50 to 92% and 80 to 100%, respectively, for K. pneumoniae. E. cloacae strains showed MIC levels ≥32 μg/mL for both agents. The AUD ratio for CMZ to FMOX ranged from 5.31 to 12.27, with no apparent upward or downward trend. Proportions of ESBL-producing E. coli and K. pneumoniae strains with MIC ≤1 μg/mL were greater in FMOX than in CMZ. To corroborate the clinical superiority of FMOX in treating ESBL-E infections, a randomized controlled study, as well as pharmacokinetic/pharmacodynamic analysis, is required.