High-dose Cefepime vs Carbapenems for Bacteremia Caused by Enterobacterales with Moderate to High Risk of Clinically Significant AmpC β-lactamase Production

Background. Limited data suggest that serious infections caused by Enterobacterales with a moderate to high risk of clinically significant AmpC production can be successfully treated with cefepime if the cefepime minimum inhibitory concentration (MIC) is ≤2 µg/mL. However, isolates with a cefepime-susceptible dose-dependent (SDD) MIC of 4–8 µg/mL should receive a carbapenem due to target attainment and extended-spectrum β-lactamase (ESBL) concerns. Methods. This was a retrospective cohort study of hospitalized patients with E. cloacae, K. aerogenes, or C. freundii bacteremia from January 2015 to March 2022 receiving high-dose cefepime or a carbapenem. Cox regression models were used with incorporation of inverse probability of treatment weighting and time-varying covariates. Results. Of the 315 patients included, 169 received cefepime and 146 received a carbapenem (ertapenem n = 90, meropenem n = 56). Cefepime was not associated with an increased risk of 30-day mortality compared with carbapenem therapy (adjusted hazard ratio [aHR], 1.45; 95% CI, 0.79–2.14), which was consistent for patients with cefepime SDD isolates (aHR, 1.19; 95% CI, 0.52–1.77). Multivariable weighted Cox models identified Pitt bacteremia score >4 (aHR, 1.41; 95% CI, 1.04–1.92), deep infection (aHR, 2.27; 95% CI, 1.21–4.32), and ceftriaxone-resistant AmpC-E (aHR, 1.32; 95% CI, 1.03–1.59) to be independent predictors associated with increased mortality risk, while receipt of prolonged-infusion β-lactam was protective (aHR, 0.67; 95% CI, 0.40–0.89). Conclusions. Among patients with bacteremia caused by Enterobacterales with moderate to high risk of clinically significant AmpC production, these data demonstrate similar risk of 30-day mortality for high-dose cefepime or a carbapenem as definitive β-lactam therapy.