ETEST Aztreonam/Avibactam (AZA) (0.016/4-256/4 µg/mL)

ETEST Aztreonam/Avibactam (AZA) is a manual quantitative antimicrobial susceptibility test strip used to determine the minimum inhibitory concentration (MIC) of the antibiotic combination aztreonam/avibactam against Enterobacterales bacteria. The plastic strip carries a predefined antibiotic gradient that transfers into agar; bacterial growth inhibition appears as an ellipse, and the MIC is read where the ellipse intersects the strip's scale.

The device contains aztreonam at concentrations from 0.016 to 256 µg/mL overlaid with a fixed 4 µg/mL of avibactam. Key similarities to the predicate (ETEST Ceftazidime/Avibactam) include identical test methodology, inoculum type, quantitative format, and identical avibactam concentration. The primary difference is substitution of aztreonam for ceftazidime and a narrower set of indicated organisms (Enterobacterales only, excluding Pseudomonas aeruginosa and some species in the predicate).

Testing followed CLSI M07-11th Edition (January 2018) broth microdilution reference method and CLSI M100 35th Edition (January 2025) specifications. The submission also adheres to the FDA Class II Special Controls Guidance Document on Antimicrobial Susceptibility Test Systems (August 28, 2009).

Substantial equivalence rests on the nearly identical test platform, methodology, and performance characteristics: both use the same ETEST strip technology with identical methodology to generate MIC values. The device achieved 95.7% essential agreement and 98.0% category agreement against the CLSI reference method across 602 Enterobacterales strains, demonstrating acceptable performance comparable to the predicate's 99.1% and 99.6% respectively. Although the antimicrobial agent differs (aztreonam vs. ceftazidime), both are beta-lactam/beta-lactamase inhibitor combinations with the same avibactam concentration, intended use is functionally identical (MIC determination), and indicated organisms substantially overlap, supporting equivalence despite the narrower organism scope.