1293. In vitro Activity of Ceftibuten in Combination with VNRX-5236 against Clinical Isolates of Enterobacterales from Urinary Tract Infections Collected in 2018-2020

Abstract Background Increasing resistance among agents commonly prescribed to treat urinary tract infections indicate that new oral agents are urgently needed. Ceftibuten in combination with VNRX-7145 is under development as an oral treatment for complicated urinary tract infections caused by serine β-lactamase-producing Enterobacterales, including isolates carrying ESBLs and carbapenemases. In vivo , VNRX-7145 (VNRX-5236 etzadroxil) is cleaved into to the active inhibitor, VNRX-5236. This study assessed the in vitro activity of ceftibuten/VNRX-5236 against 592 isolates of Enterobacterales from urinary tract infections (UTIs) from a 2018-2020 global culture collection. Methods MICs of ceftibuten with VNRX-5236 fixed at 4 µg/mL and comparators were determined following CLSI M07-A11 guidelines against 592 Enterobacterales. Isolates were from community and hospital UTI infections collected from 133 sites in 31 countries in 2018-2020. Resistant phenotypes were based on 2021 CLSI breakpoints. Results A substantial percentage of isolates were non-susceptible to extended-spectrum β-lactams, levofloxacin (LVX), trimethoprim-sulfamethoxazole (SXT), and amoxicillin-clavulanate (AMC) (Table). The addition of VNRX-5236 reduced ceftibuten MIC 90 values by ≥8-fold to ≥128-fold, depending on the resistant subset. Ceftibuten/VNRX-5236 had potent activity against all Enterobacterales, with MIC 50/90 values of 0.06/0.25 µg/mL and 98.3% inhibited at ≤2 µg/mL. Ceftibuten/VNRX-5236 maintained activity against resistant subsets (MIC 90 range, 0.5 to 2 µg/mL; 91.5% to 97.1% inhibited at ≤2 µg/mL), including serine carbapenemase-positive isolates (MIC 90 0.5 µg/mL; 100% inhibited at ≤1 µg/mL). Ceftibuten/VNRX-5236 in vitro potency was similar to that of newer parenteral and investigational oral therapies. Results TableConclusion Ceftibuten/VNRX-5236 exhibited promising in vitro activity against recent Enterobacterales from UTIs, and may have potential as an oral treatment option for complicated urinary tract infections, including those caused by serine β-lactamase-expressing Enterobacterales (ESBL, KPC, OXA-48/OXA-48-like) for which there are currently few oral treatment options available. Disclosures Meredith Hackel, PhD MPH , IHMA (Employee) Pfizer, Inc. (Independent Contractor) Mark G G. Wise, PhD , IHMA (Employee) Pfizer, Inc. (Independent Contractor) Daniel F. Sahm, PhD , IHMA (Employee) Pfizer, Inc. (Independent Contractor)