Outcomes of treating AmpC-producing Enterobacterales bacteraemia with carbapenems vs. non-carbapenems

AmpC β-lactamases are found in Enterobacter species, Serratia species, Citrobacter freundii, Providencia species and Morganella morganii (‘ESCPM’). Carbapenems are commonly used to treat severe ‘ESCPM’ infections. Carbapenem-sparing agents are needed because of increasing carbapenem resistance worldwide. Use of cefepime and piperacillin-tazobactam has limited supportive clinical data. We evaluated the efficacy of non-carbapenems vs. carbapenems in ‘ESCPM’ bacteraemia.A retrospective cohort study was conducted on patients with ‘ESCPM’ bacteraemia. Primary outcome was 30-day mortality. Analyses were performed on patients who received carbapenems vs. piperacillin-tazobactam or cefepime monotherapy as empirical and definitive therapy. Propensity score for carbapenem therapy was adjusted for in multivariate analyses for 30-day mortality.A total of 241 patients were included. The most common bacterium isolated was Enterobacter species (58.1%). Common sources were urinary (22.8%) and vascular lines (22.0%). Carbapenems (28.6%) and piperacillin-tazobactam (28.6%) were the commonest empirical antibiotics. Carbapenems (54.8%) and cefepime (23.7%) were the most common definitive antibiotics. Median Pitt bacteraemia score was 1 (interquartile range [IQR], 0-2). Overall, 30-day mortality was 12.9%.Adjusted multivariate analyses for empirical and definitive antibiotic treatment models yielded risk factors for 30-day mortality, including higher Pitt bacteraemia score (empirical: adjusted OR [aOR] 1.21 for each point increase, 95% confidence interval [CI]:1.01-1.45; definitive: aOR 1.33 for each point increase, 95% CI:1.06-1.69) and age (empirical: aOR 1.04 for each year increase, 95% CI:1.01-1.08). Empirical piperacillin-tazobactam (aOR 0.29, 95% CI:0.07-1.27) and definitive cefepime (aOR 0.65, 95% CI:0.12-3.55) were not associated with 30-day mortality.Compared with carbapenem therapy, empirical piperacillin-tazobactam and definitive cefepime were not associated with 30-day mortality in ‘ESCPM’ bacteraemia.