473: Comparison of MicroScan System Prompt and Turbidity Methods for Measuring Vancomycin Minimum inhibitory concentration (MIC) against Methicillin-resistant Staphylococcus aureus (MRSA) with MIC of 2ug/ml, the Clinical Implications and economic impact of using alternative antimicrobial agents to vancomycin for MRSA with possible MIC of 2ug/ml

Background. Vancomycin remains the mainstay of therapy for Invasive MRSA infections. IDSA guideline recommends an alternative antibiotic in patients with vancomycin MIC of 2ug/ml. There is considerable variability of MIC results depending on the method used. MicroScan method is the most commonly used in the US. Usually MicroScan report values higher than broth microdilution method and this can lead to use of alternative agents.

Methods. A single-center study comparing MicroScan Prompt method vs MicroScan Turbidity method. We collected 21 MRSA isolates from sterile sites with Vancomycin MIC of 2ug/ml measured by Prompt method. The accuracy of MIC was confirmed by repeating the Prompt method. Same isolates were tested by Turbidity method and compared with CLSI standard Broth microdilution (BMD) method. In addition, we identified 56 patients over 9 months with invasive MRSA infections with vancomycin MIC of 2 measured by prompt method and its impact on prescribing an alternative agent.

Results. Only 52.2% of MRSA isolate were 2ug/ml when Prompt method was repeated. Turbidity method by MicroScan and BMD method showed only 9.5% of MRSA isolate were 2ug/ml. MicroScan Turbidity and BMD method correlated with each other 100%. MicroScan Prompt method overcalled vancomycin MIC in 90% of MRSA isolates. Among 56 patients with invasive MRSA infection, 86% of the patients had their antibiotics changed due to MIC of 2(n= 48 of 56). Antibiotics were changed to Daptomycin (72.9%), Ceftaroline (18.7%), Clindamycin (4.1%), Linezolid (2%) and Telavancin (2%). The prices of these antibiotics in comparison to Vancomycin in multiples of Vancomycin price are Daptomycin 27, Ceftaroline 11, Clindamycin 0.3, Linezolid 25 and Telavancin 18. The average increase in cost was 16.2 times of the Vancomycin price.

Conclusion. The MicroScan Turbidity can be a cost effective method to measure vancomycin MIC and comparable to the standard BMD method. MicroScan Prompt method over calculates the Vancomycin MIC, results in overprescribing of alternative antimicrobial agents to vancomycin, increase the healthcare associated cost and risks increase of antimicrobial resistance which defies important goal in antimicrobial stewardship.

Disclosures. All authors: No reported disclosures.