In vivo efficacy of WCK 6777 (ertapenem/zidebactam) against carbapenemase-producing Klebsiella pneumoniae in the neutropenic murine pneumonia model

Objectives Ertapenem has proven to be an effective antimicrobial; however, increasing enzyme-mediated resistance has been noted. Combination with zidebactam, a beta-lactam enhancer, is restorative. Human-simulated regimens (HSRs) of ertapenem and zidebactam alone and in combination (WCK 6777; 2 g/2 g q24h) were assessed for efficacy against carbapenemase-producing Klebsiella pneumoniae (CP-KP) in the pneumonia model. Methods Infected ICR mice were rendered neutropenic and exposed to various doses of ertapenem and zidebactam alone and in combination to develop the HSRs that were subsequently confirmed in additional pharmacokinetic studies. Twenty-one CP-KP (KPC or OXA-48-like producers) with WCK 6777 MICs of 1-8 mg/L were utilized. Mice were treated for 24 h with saline or HSRs of ertapenem, zidebactam and WCK 6777. Efficacy was defined as change in mean lung bacterial density relative to 0 h. Results Confirmatory pharmacokinetic analysis showed agreement between predicted human exposures (%fT(>MIC)) and those achieved in vivo for all three HSRs. The 0 h bacterial density across all isolates was 6.69 +/- 0.31 log(10) cfu/lungs. At 24 h, densities increased by 2.57 +/- 0.50, 2.2 +/- 0.60 and 2.05 +/- 0.71 log(10) cfu/lungs in the 24 h control, ertapenem HSR and zidebactam HSR groups, respectively. Overall, 18/21 of the isolates exposed to the WCK 6777 HSR displayed a killing profile that exceeded the translational benchmark for efficacy of a 1 log(10) cfu reduction. Among the remaining three isolates, two displayed similar to 0.5 log(10) kill and stasis was observed in the third. Conclusions Human-simulated exposures of WCK 6777 demonstrated potent in vivo activity against CP-KP, including those with WCK 6777 MICs up to 8 mg/L.