Below are the CLSI breakpoints for selected bacteria. Please use your clinical judgement when assessing breakpoints. The lowest number does NOT equal most potent antimicrobial. Contact Antimicrobial Stewardship for drug selection and dosing questions.

Table 1: 2014 MIC Interpretive Standards for Enterobacteriaceae (includes E.coli, Klebsiella, Enterobacter, Citrobacter, Serratia and Proteus spp) Antimicrobial Agent MIC Interpretive Criteria (g/mL) Enterobacteriaceae S I R Ampicillin ≤ 8 16 ≥ 32 Ampicillin-sulbactam ≤ 8/4 16/8 ≥ 32/16 Aztreonam ≤ 4 8 ≥ 16 Cefazolin (blood) ≤ 2 4 ≥ 8 Cefazolin** (uncomplicated UTI only) ≤ 16 ≥ 32 Cefepime* ≤ 2 4-8* ≥ 16 Cefotetan ≤ 16 32 ≥ 64 Ceftaroline ≤ 0.5 1 ≥ 2 Ceftazidime ≤ 4 8 ≥ 16 Ceftriaxone ≤ 1 2 ≥ 4 Cefpodoxime ≤ 2 4 ≥ 8 Ciprofloxacin ≤ 1 2 ≥ 4 Ertapenem ≤ 0.5 1 ≥ 2 Fosfomycin ≤ 64 128 ≥256 Gentamicin ≤ 4 8 ≥ 16 Imipenem ≤ 1 2 ≥ 4 Levofloxacin ≤ 2 4 ≥ 8 Meropenem ≤ 1 2 ≥ 4 Piperacillin-tazobactam ≤ 16/4 32/4 – 64/4 ≥ 128/4 Trimethoprim-sulfamethoxazole ≤ 2/38 --- ≥ 4/76 *Susceptibile dose-dependent – see chart below **Cefazolin can predict results for cefaclor, cefdinir, cefpodoxime, cefprozil, cefuroxime axetil, cephalexin and loracarbef for uncomplicated UTIs due to E.coli, K.pneumoniae, and P.mirabilis. Cefpodoxime, cefinidir, and cefuroxime axetil may be tested individually because some isolated may be susceptible to these agents while testing resistant to cefazolin.

Cefepime dosing for Enterobacteriaceae ( E.coli, Klebsiella, Enterobacter, Citrobacter, Serratia & Proteus spp) Susceptible Susceptible –dose-dependent (SDD) Resistant MIC /= 16 Based on dose of: 1g q12h 1g every 8h or 2g every 8 h Do not give 2g q12 Total dose 2g 3-4g 6g NA

Table 2: 2014 MIC Interpretive Standards for Pseudomonas aeruginosa and Acinetobacter spp. Antimicrobial Agent MIC Interpretive Criteria (g/mL) Pseudomonas aeruginosa S I R Amikacin ≤ 16 32 ≥ 64 Aztreonam ≤ 8 16 ≥ 32 Cefepime ≤ 8 16 ≥ 32 Ceftazdime ≤ 8 16 ≥ 32 Ciprofloxacin ≤ 1 2 ≥ 4 Colistin/Polymixin B(Pseudomonas) ≤ 2 4 ≥ 8 Colistin/ Polymixin B (Acinetobacter) ≤ 2 ≥ 4 Gentamicin ≤ 4 8 ≥ 16 Imipenem ≤ 2 4 ≥ 8 Levofloxacin ≤ 2 4 ≥ 8 Meropenem ≤ 2 4 ≥ 8 Minocycline (Acinetobacter only) ≤ 4 8 ≥ 16 Piperacillin-tazobactam ≤ 16/4 32/4 – 64/4 ≥ 128/4 Ticarcillin-clavulanic acid ≤ 16/2 32/2 – 64/2 ≥ 128/2 Tobramycin ≤ 4 8 ≥ 16

GRAM POSITIVES Table 3: 2014 MIC Interpretive Standards for S.aureus. Antimicrobial Agent MIC Interpretive Criteria (g/mL) S.aureus S I R Ceftaroline ≤ 1 2 ≥ 4 Clindamycin ≤ 0.5 1-2 ≥ 4 Erythromycin ≤ 0.5 1-4 ≥ 8 Gentamicin ≤ 4 8 ≥ 16 Levofloxacin ≤ 1 2 ≥ 4 Moxifloxacin ≤ 0.5 1 ≥ 2 Oxacillin* ≤ 2 ≥ 4 Penicillin ≤ 0.12 ≥ 0.25 Rifampin ≤ 1 2 ≥ 4 Tetracycline ≤ 4 8 ≥ 16 Trimethoprim/Sulfamethoxazole ≤ 2/38 ≥ 4/76 Vancomycin ≤ 2 4-8 ≥ 16 Daptomycin ≤ 1 Linezolid ≤ 4 ≥ 8 *Rifampin should not be used for monotherapy ** If oxacillin susceptible, then results can applied to other beta-lactams including cephalosporins.

Table 4: 2014 MIC Interpretive Standards for Enterococcus species.

Antimicrobial Agent MIC Interpretive Criteria (g/mL) Enterococcus spp S I R Ampicillin*** ≤ 8 ≥ 16 Daptomycin ≤ 4 Doxycycline ≤ 4 8 ≥ 16 Erythromycin ≤ 0.5 1-4 ≥ 8 Gentamicin Synergy or no synergy Linezolid ≤ 2 4 ≥ 8 Penicillin** ≤ 8 ≥ 16 Quinapristin-dalfopristin ≤ 1 2 ≥ 4 (Synercid) Rifampin ≤ 1 2 ≥ 4 Streptomycin Synergy or no synergy Vancomycin ≤ 4 8-16 ≥ 32 *For enterococcus, cephalosporins, aminoglycosides (except for high-level resistance screening), clindamycin, and trimethoprim- sulfamethoxazole are not effective clinically.

**Call microbiology lab for penicillin MIC.

***Ampicillin susceptibility testing predicts activity of amoxicillin, amoxicillin-clavulanate, ampicillin-sulbactam, piperacillin, and piperacillin-tazobactam. Ampicillin susceptibility can be used to predict imipenem susceptibility provided the species is E.faecalis.