Establishing the reference broth microdilution MIC method for cefepime-taniborbactam.

The investigational β-lactam/β-lactamase inhibitor combination cefepime-taniborbactam is intended as therapy for serious infections caused by Gram-negative pathogens resistant to third-generation cephalosporins and carbapenems. Establishing a susceptibility testing reference method for cefepime-taniborbactam that conforms to the Clinical Laboratory Standards Institute (CLSI) M07 and International Standards Organization 20776-1:2019 standards is necessary to inform patient care. This study describes the reference broth microdilution MIC method for cefepime-taniborbactam (taniborbactam fixed at 4 µg/mL). In a CLSI M23 Tier 2 study that included nine clinical microbiology laboratories, the CTX-M-15-producer Escherichia coli NCTCC 13353 was determined to be appropriate for routine quality control (QC) as ranges for cefepime (≥64 µg/mL) and cefepime-taniborbactam (0.12 to 1 µg/mL) were non-overlapping, thereby simultaneously controlling for cefepime antibacterial activity and taniborbactam β-lactamase inhibition. Of the cefepime-taniborbactam MIC results obtained, 99.6% (269/270) were within the identified QC range; similarly, 100% (79/79) and 98.0% (98/100) of the QC values from a surveillance study and from the two central microbiology laboratories of the CERTAIN-1 Phase 3 clinical study (clintrials.gov identifier NCT03840148) were in range, respectively. Modifications to the standard medium (pH, cation content, or supplementation with human serum, albumin, polysorbate-80, or pulmonary surfactant) or assay parameters (inoculum density, incubation duration, and atmosphere) revealed that only inoculum titers (e.g., ≥5 × 10⁶ CFU/mL) exceeding the CLSI M07 standard (2-8 × 10⁵ CFU/mL) increased MIC values above the QC range. These results demonstrate the robustness and reliability of the cefepime-taniborbactam broth microdilution MIC reference method when performed following the approved standards.

Importance: This study focuses on a new antibiotic combination called cefepime-taniborbactam that is being developed to treat serious infections caused by bacteria that are often resistant to current treatments. To make sure this new antibiotic combination can be used safely and effectively once it has been approved for clinical use, we developed a standardized laboratory method to measure its activity against certain bacteria that are widely used during quality control testing. The method was assessed in multiple labs and proved to be reliable, accurate, and consistent. It also held up well under different testing conditions, showing that it is a dependable tool for guiding treatment decisions. This is an important step in meeting the challenge of antibiotic-resistant infections since it will help clinicians evaluate cefepime-taniborbactam as a potential treatment option as they strive to improve the care of patients suffering from serious infections.