Comparative effectiveness of flomoxef versus carbapenems in the treatment of bacteraemia due to extended-spectrum β-lactamase-producing Escherichia coli or Klebsiella pneumoniae with emphasis on minimum inhibitory concentration of flomoxef: a retrospecti

This study compared treatment outcomes of adult patients with bacteraemia due to extended-spectrum β-lactamase-producing Escherichia coli or Klebsiella pneumoniae (ESBL-EK) receiving flomoxef versus those receiving a carbapenem as definitive therapy. In propensity score matching (PSM) analysis, case patients receiving flomoxef shown to be active in vitro against ESBL-EK were matched with controls who received a carbapenem. The primary endpoint was 30-day crude mortality. The flomoxef group had statistically significantly higher sepsis-related mortality (27.3% vs. 10.5%) and 30-day mortality (28.8% vs. 12.8%) than the carbapenem group. Of the bacteraemic episodes caused by isolates with a MICflomoxef of ≤1 mg/L, sepsis-related mortality rates were similar between the two treatment groups (8.7% vs. 6.4%; P = 0.73). The sepsis-related mortality rate of the flomoxef group increased to 29.6% and 50.0% of episodes caused by isolates with a MICflomoxef of 2-4 mg/L and 8 mg/L, respectively, which was significantly higher than the carbapenem group (12.3%). In the PSM analysis of 86 case-control pairs infected with strains with a MICflomoxef of 2-8 mg/L, case patients had a significantly higher 30-day mortality rate (38.4% vs. 18.6%). Multivariate regression analysis revealed that flomoxef therapy for isolates with a MICflomoxef of 2-8 mg/L, concurrent pneumonia or urosepsis, and a Pitt bacteraemia score ≥4 were independently associated with 30-day mortality. Definitive flomoxef therapy appears to be inferior to carbapenems in treating ESBL-EK bacteraemia, particularly for isolates with a MICflomoxef of 2-8 mg/L, even though the currently suggested MIC breakpoint of flomoxef is ≤8 mg/L.