In vivo efficacy of meropenem with a novel non--lactam–-lactamase inhibitor, nacubactam, against gram-negative organisms exhibiting various resistance mechanisms in a murine complicated urinary tract infection model

Urinary tract infections (UTIs) are a tremendous burden on the health care system due to the vast number of infections resulting in antibiotic therapy and/or hospitalization. Additionally, these infections are frequently caused by multidrug-resistant (MDR) organisms, limiting the availability of effective antimicrobials. Nacubactam is a novel non--lactam--lactamase inhibitor with in vitro activity against class A and class C -lactamases. Nacubactam is being developed in combination with meropenem, providing broad-spectrum activity in addition to improved stability against common -lactamases. Here, we utilized a neutropenic murine complicated UTI (cUTI) model to determine the potential clinical utility of meropenem-nacubactam compared with meropenem or nacubactam alone against 10 Klebsiella pneumoniae, Escherichia coli, and Enterobacter cloacae isolates with diverse genotypic and phenotypic profiles, including NDM, KPC, OXA, CTX-M, SHV, and TEM enzyme-producing isolates. Selected isolates had meropenem-nacubactam MICs between 1 and 8 g/ ml. Meropenem-nacubactam demonstrated the greatest in vivo efficacy against 9 of 10 isolates, achieving a 3 log reduction from the 48-h control in all isolates tested, including isolates prepared as high inoculums. Nacubactam alone confirmed antibacterial properties, achieving a 1 log reduction against the majority of isolates. The combination of meropenem-nacubactam further enhanced the activity of either agent alone, notably against meropenem-resistant isolates. Against ceftazidime-avibactam-resistant isolates, meropenem-nacubactam demonstrated increased antibacterial kill upwards of 6 log ₁₀ CFU in comparison to the 48-h control. Our data support the potential clinical utility of meropenem-nacubactam for cUTI in humans against MDR Enterobacteriaceae, although further clinical data supporting meropenem-nacubactam efficacy are needed.