Outcomes of treating AmpC producing Enterobacterales bacteraemia with Carbapenems versus Non-carbapenems

Abstract Introduction AmpC β-lactamases are found in Enterobacter species, Serratia species, Citrobacter freundii, Providencia species and Morganella morganii (‘ESCPM’). Carbapenems are commonly used in treatment for severe ‘ESCPM’ infections. Carbapenem-sparing agents are needed with increasing carbapenem resistance worldwide. Use of cefepime and piperacillin-tazobactam have limited supportive clinical data. We evaluated efficacy of non-carbapenems versus carbapenems in ’ESCPM’ bacteraemia. Methods 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 versus piperacillin-tazobactam or cefepime monotherapy as empiric and definitive therapy. Propensity score for carbapenem therapy was adjusted for in multivariate analyses for 30-day mortality. Results Two hundred and forty-one patients were included. Commonest 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 empiric antibiotics. Carbapenems (54.8%) and cefepime (23.7%) were the commonest definitive antibiotics. Median Pitt bacteraemia score was 1 (IQR, 0-2). Overall, 30-day mortality was 12.9%. Adjusted multivariate analyses for empiric and definitive antibiotic treatment models yielded risk factors for 30-day mortality including higher Pitt bacteraemia score (empiric: adjusted OR (aOR) 1.21 for each point increase, 95% CI:1.01-1.45; definitive: aOR 1.33 for each point increase, 95% CI:1.06-1.69) and age (empiric: aOR 1.04 for each year increase, 95% CI:1.01-1.08). Empiric 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. Conclusions Compared to carbapenem therapy, empiric piperacillin-tazobactam and definitive cefepime were not associated with 30-day mortality in ’ESCPM’ bacteraemia.