A Systematic Approach to the Selection of the Appropriate Avibactam Concentration for Use with Ceftazidime in Broth Microdilution Susceptibility Testing.

Selection of the avibactam concentration to combine with ceftazidime in susceptibility testing was determined using Gram-negative isolates with characterized β-lactamases predefined as susceptible or resistant, based on the known inhibition spectrum of avibactam. MIC values were determined by broth microdilution of ceftazidime with fixed concentrations and ratios of avibactam. A constant concentration of 4 μg/ml of avibactam was selected for susceptibility testing with ceftazidime because of its ability to correctly categorize susceptible and resistant isolates while minimizing categorical errors.