590. Activities of Cefepime-Taniborbactam and Ceftazidime-Avibactam against Cefepime-Resistant Respiratory Gram-Negative Pathogens in a Hollow Fiber Infection Model

Abstract Background Cefepime-taniborbactam (FTB) combines cefepime (FEP), a fourth generation cephalosporin with taniborbactam, a novel inhibitor of metallo (MBL)- and serine β-lactamases (SBL). FTB 2.5g IV q8h was safe and effective in adults with complicated urinary tract infection in a Phase 3 trial (NCT03840148). FTB is also under development for hospital-acquired and ventilator-associated bacterial pneumonia (HABP/VABP). Methods An in vitro hollow fiber infection model (HFM) was used to assess resistance emergence in MBL- and/or SBL-producing Klebsiella pneumoniae (KP, n=5) and Pseudomonas aeruginosa (PA, n=3) treated with humanized exposures of FTB or ceftazidime-avibactam (CZA). Dense (≥ 7 log10 CFU/mL) log phase cultures were inoculated into HFM cartridges and treated with human equivalent doses of FEP (2g q8h), FTB (2.5g q8h), or CZA (2.5g q8h) for 4 days. KP strains collectively harbored NDM (n=2), VIM (n=1), CTX-M (n=4), SHV-ESBL (n=1), CMY (n=1), KPC (n=1), and OXA-48 (n=1). PA strains produced either VIM (n=1), CTX-M (n=1), or KPC (n=1). Pharmacokinetic profiles of FTB and CZA in HFMs, based on free drug exposures in plasma of healthy volunteers, were confirmed by LC-MS/MS. For CZA HFMs with MBL-producing strains, EDTA was added to sequester zinc to restore CZA susceptibility (MIC ≤ 8 mg/L). Viable bacteria were quantitated by serial dilution plating; subpopulations with elevated MICs (≥ 4x) were monitored on FTB- or CZA-supplemented agar. Results FEP, FTB, and CZA MICs ranged 16 to > 128 mg/L, 0.5–8 mg/L, and 2 to > 128 mg/L, respectively. FEP was inactive (n=7) or bacteriostatic (n=1, FEP MIC=16 mg/L). FTB was bactericidal (≥ 3 log kill) against all 8 strains; subpopulations with elevated FTB MICs were not detected. Against MBL producers, CZA was inactive without EDTA and was bacteriostatic (n=2) or bactericidal (n=2) only when EDTA was added to disable MBLs. Against non-MBL producers, all of which were CZA-susceptible, CZA was either bactericidal (n=1) or bacteriostatic (n=2) or allowed growth due to emergence of resistance (n=1). Conclusion Humanized exposures of FTB in a HFM were bactericidal against high inocula of MBL- and/or SBL-producing, multidrug-resistant respiratory pathogens and prevented emergence of resistance for 4 days. The results support development of FTB for HABP/VABP. Disclosures Lindsay M. Avery, PharmD, Venatorx Pharmaceuticals: Employee|Venatorx Pharmaceuticals: Stocks/Bonds Lindsay M. Avery, PharmD, Venatorx Pharmaceuticals: Employee|Venatorx Pharmaceuticals: Stocks/Bonds Mitchell Edwards, n/a, Venatorx Pharmaceuticals: Employee|Venatorx Pharmaceuticals: Stocks/Bonds Fan Yi, PhD, Venatorx Pharmaceuticals: Employee|Venatorx Pharmaceuticals: Stocks/Bonds Philip E. Sabato, PharmD, MS, Venatorx Pharmaceuticals: Employee|Venatorx Pharmaceuticals: Stocks/Bonds Greg Moeck, PhD, Venatorx Pharmaceuticals: Employee|Venatorx Pharmaceuticals: Stocks/Bonds Daniel C. Pevear, PhD, Venatorx Pharmaceuticals: Employee|Venatorx Pharmaceuticals: Stocks/Bonds.