Resurgence of Polymyxin B for MDR/XDR Gram-Negative Infections: An Overview of Current Evidence

Table 1

Susceptibility breakpoints of polymyxins for major pathogens.

Organism	Profile
	Susceptible	Intermediate	Resistant
CLSI recommendations [18]
P. aeruginosa	MIC ≤ 2 mg/L	MIC = 4	MIC ≥ 8 mg/L
Acinetobacter	MIC ≤ 2 mg/L	—	MIC ≥ 4 mg/L
Non-Enterobacteriaceae	MIC ≤ 2 mg/L	MIC = 4	MIC ≥ 8 mg/L
BSAC Recommendations [19]
Pseudomonas spp.^#	MIC ≤ 4 mg/L	—	MIC ≥ 8 mg/L
Enterobacteriaceae spp.^#	MIC ≤ 4 mg/L	—	MIC ≥ 8 mg/L

For colistin and polymyxin B; for colistin only. MIC: minimum inhibitory concentration; CLSI: Clinical and Laboratory Standards Institute; BSAC: British Society for Antimicrobial Chemotherapy.