181. Correlation between Vancomycin Utilization and Methicillin-resistant Staphylococcus aureus (MRSA) Blood Culture Isolate MIC
Session: Poster Abstract Session: Antimicrobial Stewardship: Current State and Future Opportunities
Thursday, October 8, 2015
Room: Poster Hall
  • IDSA 2015 MRSA 10_5_2015.pdf (383.3 kB)
  • Background: The treatment of choice for MRSA bacteremia (MRSAB) is vancomycin, however failures have occurred when the MRSA MIC to vancomycin is 2 mcg/ml.  MIC values of 2 mcg/ml are being reported with increasing frequency in the literature.  Also of potential concern are vancomycin-susceptible S.aureus (VSSA) with an elevated MIC of 1 mcg/ml.  At our institution, between the Fiscal years 2011-2014, 3.7% of MRSA blood isolates had a vancomycin MIC of 2 mcg/ml, and 60% had an MIC of 1 mcg/ml.  Moreover, high rates of antimicrobial utilization may create selective pressure for reduced antibiotic susceptibilities.  We therefore sought to determine if there is an identifiable correlation between vancomycin utilization and rates of elevated vancomycin MIC values at our hospital.  

    Methods: All MRSA blood culture isolates obtained between Fiscal year (FY) 2011 to 2014 were included, and compared to vancomycin utilization defined by mean duration (days) vancomycin/case (reflective of our overall utilization, not specific to use for MRSAB).  Vancomycin MIC was determined by broth microdilution (Vitek-2).  Only the first MRSA blood isolate per patient per analysis period was counted.

    Results: The mean duration (days) vancomycin/case per FY and the number of isolates with an MIC of 1 and 2 mcg/ml are shown in Table 1.  The correlation coefficient (R2) between vancomycin utilization was 0.9 for an MIC of 2 mcg/ml (Figure 1), and 0.6 for MIC 1 mcg/ml (Figure 2).

    Table 1:





    MIC 1 mcg/ml





    MIC 2 mcg/ml





    Mean duration (days) vancomycin/case





    \s \s

    Conclusion: We identified a correlation between vancomycin utilization and the occurrence of MRSA blood isolate MIC values of 1 and 2 mcg/ml.  An important limitation of this analysis is that the data are aggregate and do not account for appropriateness of therapy.  Nonetheless, these results highlight the importance of antimicrobial stewardship efforts in ensuring appropriate utilization of vancomycin to minimize the occurrence of MRSA blood isolates with elevated MIC values.

    Natasha Pettit, PharmD1, Zhe Han, PharmD1, Kathleen G. Beavis, MD2, Jennifer M. Pisano, MD3 and Angella Charnot-Katsikas, MD4, (1)Pharmacy Services, The University of Chicago Medicine, Chicago, IL, (2)Microbiology, The University of Chicago Medicine, Chicago, IL, (3)Infectious Diseases and Global Health, The University of Chicago Medicine, Chicago, IL, (4)Pathology, The University of Chicago Medicine, Chicago, IL


    N. Pettit, None

    Z. Han, None

    K. G. Beavis, None

    J. M. Pisano, None

    A. Charnot-Katsikas, None

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