Determination of MIC Quality Control Ranges for Ceftibuten-Avibactam (Fixed 4 μg/mL), a Novel β-Lactam/β-Lactamase Inhibitor Combination

ABSTRACT Ceftibuten/ARX-1796 (avibactam prodrug) is a novel oral antibacterial combination in early clinical development for the treatment of complicated urinary tract infections (cUTI) including pyelonephritis. ARX-1796 is the novel avibactam prodrug being combined with ceftibuten for oral dosing that is converted to active avibactam in vivo. A Clinical and Laboratory Standards Institute (CLSI) M23 (2018) tier 2 broth microdilution quality control (QC) study was conducted with ceftibuten-avibactam to establish MIC QC ranges. Ceftibuten-avibactam broth microdilution QC ranges were approved for Escherichia coli ATCC 25922 (0.016/4 to 0.12/4 μg/mL), E. coli NCTC 13353 (0.03/4 to 0.12/4 μg/mL), Klebsiella pneumoniae ATCC 700603 (0.06/4 to 0.25/4 μg/mL), K. pneumoniae ATCC BAA-1705 (0.03/4 to 0.25/4 μg/mL), and K. pneumoniae ATCC BAA-2814 (0.12/4 to 0.5/4 μg/mL) by the CLSI Subcommittee on Antimicrobial Susceptibility Testing in January 2022. Approved ceftibuten-avibactam QC ranges will support future clinical development, device manufacturers, and routine patient care.

Ceftibuten is a semisynthetic third-generation oral cephalosporin approved by the United States Food and Drug Administration in 1995 for the treatment of acute bacterial exacerbations of chronic bronchitis, acute bacterial otitis media, and pharyngitis and tonsillitis caused by indicated organisms (6). Ceftibuten has also been used clinically in the treatment of complicated and uncomplicated urinary tract infections, although these are not approved indications (7,8). The effectiveness of cephalosporins, including ceftibuten, against Enterobacterales isolates has diminished due to the emergence and spread of ESBL-and carbapenemase (KPC and OXA-48)producing isolates. Ceftibuten/ARX-1796 (avibactam prodrug) is a new orally active antibacterial combination in early clinical development possessing potent in vitro activity against ESBL-, KPC-, OXA-48-, and AmpC-producing Enterobacterales isolates, including those causing urinary tract infections (9-11; H. S. Sader, C. G. Carvalhaes, M. D. Huband, R. E. Mendes, and M. Castanheira,12). ARX-1796 is the novel prodrug of avibactam being combined with ceftibuten for oral dosing that is converted to active avibactam in vivo.

MATERIALS AND METHODS
Broth microdilution. This broth microdilution quality control study for ceftibuten-avibactam followed CLSI M23 (13) tier 2 guidelines for studies requiring a multilaboratory investigation. Concurrent testing of ceftibuten and ceftazidime-avibactam was included as an experimental control. Eight qualified laboratories contributed MIC results for this study, each representing a separate and distinct institution (Table 1). Each participating laboratory utilized 3 lots of cation-adjusted Mueller-Hinton broth (CAMHB) meeting ISO/TS 16782:2016 criteria (14) obtained from 3 different commercial manufacturers (13). Commercial medium manufacturers consisted of Difco (Detroit, MI, USA; lot 9156821, medium A), BD (BBL; Sparks, MD, USA; lot 0252344, medium B), and Oxoid (Hampshire, UK; lot 3163254, medium C). Frozen-form MIC panels (lots CML1FJPT and CML1FJQR) containing ceftibuten (range tested, 512 RangeFinder is an Excel-based spreadsheet developed by Turnidge and Bordash (17) containing embedded macros that perform statistical analysis calculations on the broth microdilution MIC data submitted by the laboratories participating in CLSI M23 (13) tier 2 studies. The statistical calculations included mean, median, and modal MIC values as well as the geometric mean. For MIC data from a participating laboratory to be excluded from the overall data analysis for a particular organism/drug combination, at least 2 or more of the calculated statistical values (mean, median, and/or modal MIC) needed to be designated by the RangeFinder program as statistical outliers. In this study, no statistical outliers were identified, and no laboratories were excluded from the data analysis.
Data availability. Data will be made available upon reasonable request.

RESULTS
The CLSI M23 (13) tier 2 QC study design provides the opportunity to establish reproducible QC ranges that encompass the variability inherent in antibacterial susceptibility  testing while also accounting for differences in microbiology media. The results of this study supported the recent establishment of the ceftibuten, ceftibuten-avibactam, and ceftazidime-avibactam QC ranges as shown in Table 2 and Fig. 1 to 9.
Ceftibuten. Applying CLSI M23 (13) criteria and the RangeFinder statistical program to establish QC ranges, 99.2% (238/240) of the ceftibuten MIC results against K. pneumoniae ATCC 700603 were within the approved 3-dilution QC range of 0.25 to 1 mg/ mL ( Table 2 and Fig. 1). A 54.5% ceftibuten MIC shoulder was observed at 1 mg/mL. This MIC shoulder is below the 60.0% threshold required to expand the dilution range to 4 dilutions.

DISCUSSION
Increasing Gram-negative bacterial resistance to conventional oral antibacterials, including ciprofloxacin, nitrofurantoin, and trimethoprim-sulfamethoxazole, in patients with urinary tract infections has created a medical need for new treatment options (5). Several antibacterial agents and agent combinations with an oral treatment option are currently in clinical development for uncomplicated and/or complicated urinary tract infections including ceftibuten/ARX-1796 (avibactam prodrug), cefpodoxime-ETX0282, ceftibuten/ledaborbactam, ceftibuten-xeruborbactam, sulopenem, and tebipenem. Each of these agents and agent combinations has demonstrated potent in vitro antibacterial activity against Enterobacterales isolates from patients with urinary tract infec- tions, including extended-spectrum b-lactamase (ESBL)-producing and carbapenemresistant strains (18)(19)(20)(21)(22).
Ceftibuten is an orally active third-generation cephalosporin originally approved by the U.S. FDA in December 2015 for treatment of acute exacerbations of chronic bronchitis, otitis media, pharyngitis, and tonsilitis caused by Haemophilus influenzae, Haemophilus parainfluenzae, Moraxella catarrhalis, and penicillin-susceptible Streptococcus pneumoniae. Tested alone, ceftibuten is active against many Gramnegative pathogens and has demonstrated clinical efficacy in the treatment of uncomplicated and complicated urinary tract infections (23). The addition of the orally active avibactam prodrug (ARX-1796) to ceftibuten expands its Gram-negative antibacterial spectrum to include more recent ESBL (CTX-M)-and carbapenemase (KPC and OXA-48)-producing Enterobacterales isolates.