EUCAST MIC Breakpoints

Antimicrobial breakpoint tables to interpret MIC values

Organism
Antimicrobial
RESULTS

Pseudomonas spp. » Piperacillin-tazobactam

SUSCEPTIBLE RESISTANT
≤ 16 mg/L > 16 mg/L

Breakpoints are based on high dose therapy (with or without tazobactam, 4 g x 4).

About This Calculator

An MIC (minimum inhibitory concentration) is the lowest drug concentration at which a given antimicrobial inhibits the growth of a particular organism. MIC breakpoints are MICs at which an organism should be considered susceptible, intermediate, or resistant.

MIC Breakpoints

Organizations, such as EUCAST (in Europe) and CLSI (in the United States), publish MIC breakpoint interpretations based on pharmacokinetic/pharmacodynamic data and clinical studies. These breakpoints typically are categorized into three groups: 1,2

  • Susceptible: The organism should respond to therapy using recommended antimicrobial dosage for the given site of infection and species.
  • Intermediate: The organism's MIC approaches or exceeds the threshold for normal antimicrobial dosing, but clinical response is possible with higher doses or if the antimicrobial concentrates at the site of infection.
  • Resistant: The patient's organism should NOT be inhibited by concentrations achieved with normal dosing.

The "90-60" Rule

Generally speaking, "susceptible" infections respond to appropriate therapy approximately 90% of the time, whereas "resistant" infections respond only 60% of the time.2 With that said, patient-specific and pharmacokinetic factors have significant weight in determining clinical success.

EUCAST Breakpoints

These MIC tables are based on the 2017 EUCAST breakpoint tables.3 These tables are publically available for free on the EUCAST clinical breakpoints page. It should be noted that in the United States, most microbiology laboratories use the CLSI, not EUCAST, interpretive criteria for MICs.

CLSI Breakpoints

Like EUCAST, CLSI breakpoints are updated on a yearly basis and are commonly used by microbiology laboratories in the United States. Historically, the CLSI breakpoints were not available for free; however, in 2016 the CLSI group did release a read-only web version of their breakpoints (M100 document). Unlike EUCAST, the CLSI document is not released in a format that is easily converted into a database format, and therefore will not appear on this website.

References and Additional Reading

  1. Jorgensen JH, Ferraro MJ. Antimicrobial susceptibility testing: a review of general principles and contemporary practices. Clin Infect Dis. 2009;49(11):1749-55. PMID 19857164
  2. Kuper KM, Boles DM, Mohr JF, Wanger A. Antimicrobial susceptibility testing: a primer for clinicians. Pharmacotherapy. 2009;29(11):1326-43. PMID 19857149
  3. Clinical breakpoints (Bacterial v7.1 and Fungal v8.1). The European Committee on Antimicrobial Susceptibility Testing: http://www.eucast.org/clinical_breakpoints. Published March 3, 2017 (bacteria) and March 2, 2017 (fungi). Accessed April 10, 2017.

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Updated Apr 10, 2017
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