1405. Efficacy of the Human-Simulated Regimen (HSR) of Cefepime (FEP)/VNRX-5133 Combination Against Serine β-Lactamase-Producing Gram-negative Bacteria in the Neutropenic Murine Thigh Infection Model

BACKGROUND: VNRX-5133 is a new-generation β-lactamase inhibitor with potent activity against serine and metallo-β-lactamases. FEP/VNRX-5133 combination shows remarkable in vitro activity against multi-drug-resistant Gram-negative bacteria. The objective of this study was to assess the in vivo efficacy of HSR of the combination against a range of Enterobacteriaceae and Pseudomonas aeruginosa isolates expressing serine β-lactamases in the murine thigh infection model. METHODS: Twenty-four Enterobacteriaceae and P. aeruginosa clinical isolates producing KPC and extended-spectrum β-lactamases as well as P. aeruginosa with AmpC overexpression were utilized for in vivo studies. FEP and FEP/VNRX-5133 MIC ranges were 256 to >512 and 0.125––16 mg/L, respectively. ICR mice were rendered transiently neutropenic, and the thighs were inoculated with bacterial suspensions of 10(7) CFU/mL. HSR of FEP and VNRX-5133 equivalent to clinical doses of 2 g and 500 mg, respectively, each given q8h as 2 hours infusion were developed in the murine model. Treatment mice were administered either FEP HSR alone, FEP HSR + VNRX-5133 HSR combination, or FEP HSR + 1/8th the doses of VNRX-5133 HSR. Control mice were vehicle-dosed. Efficacy was assessed as the change in log(10)CFU/thigh at 24 hours compared with 0 hour. RESULTS: The average log(10)CFU/thigh at 0 hour across all isolates was 5.74 ± 0.53. At 24 hours, the bacterial burden increased by an average of 3.27 ± 0.53 log(10) CFU/thigh in the untreated control mice. Treatment with FEP alone was associated with average net growth of 2.76 ± 0.75 log(10)CFU/thigh. The co-administration of VNRX-5133 HSR was adequate to attain ≥ 2-log reduction in initial bacterial burdens at 24 hours in seven out of 24 isolates and ≥ 1-log reduction in the remaining 17 isolates. Furthermore, FEP HSR + 1/8th VNRX-5133 HSR resulted in ≥1-log reduction in the initial bacterial burden in 16 out of 24 isolates. CONCLUSION: FEP/VNRX-5133 combination showed potent in vivo efficacy against serine β-lactamase-producing Gram-negative isolates. The extent of bacterial killing achieved with 1/8th VNRX-5133 HSR attested to the robustness of the inhibitor activity. These data support the consideration of FEP/VNRX-5133 combination for the treatment of serious infections due to these organisms in clinical trials. DISCLOSURES: D. P. Nicolau, VenatoRx Pharmaceuticals, Inc.: Grant Investigator, Research grant