TABLE 2.

CLSI M23 Criteria used by CLSI to determine if a breakpoint warrants reevaluation for possible revision

Criterion	Example of recent revisions
Recognition of a new resistance mechanism(s)	Carbapenems for Enterobacteriaceae
New PK/PD data indicate an existing breakpoint is too high/low	Fluoroquinolones for Enterobacteriaceae and P. aeruginosa
Recognition that the antimicrobial dosage regimens used in widespread clinical practice differ substantially from the dosage regimens that were used to establish previous breakpoints	Cefazolin for Enterobacteriaceae
Introduction of new formulations of the antimicrobial agent, which result in different PK characteristics	Ceftaroline for S. aureus
New data emerge to demonstrate the previous breakpoints were not optimal for common uses of an antimicrobial agent	Penicillin for Streptococcus pneumoniae (infections other than meningitis)
New data demonstrate poor prediction of clinical response using previous breakpoints	Daptomycin for Enterococcus spp.; Piperacillin-tazobactam for P. aeruginosa
A specific public health need is identified that is not addressed by previous breakpoints	Colistin for P. aeruginosa and Acinetobacter spp.; carbapenems for Enterobacteriaceae; aztreonam and cephalosporins for Enterobacteriaceae
Significant rates of discordance are documented between MIC and disk diffusion test results when testing recent clinical isolates	Ceftaroline for S. aureus (initial reason for investigation of breakpoint)
Changes are made to CLSI-approved reference methods that affect the initial breakpoints	No recent breakpoint revisions were due to changes in CLSI reference methods
Revised breakpoints to simplify testing and eliminate need for additional tests to detect specific resistance mechanisms	Cephalosporins for Enterobacteriaceae (ESBLs)
Differences exist between breakpoints established by CLSI and those of other regulatory organizations responsible for determining breakpoints (e.g., EUCAST)	Fluoroquinolones for Enterobacteriaceae and P. aeruginosa