This information is provided by:
Susan M. Poutanen, MD, MPH, FRCPC
Editorial Board Member for the CAN-R Website
Clinical Laboratory Standards Institute (CLSI) vancomycin breakpoints for Staphylococcus aureus suggest
isolates with vancomycin MICs ≤ 2 mg/L are vancomycin-susceptible. However, evidence suggests clinical outcomes
in patients with infections due to S. aureus with vancomycin MICs or 1 or 2 are worse than those with
vancomycin MICs < 1 mg/L.
There has been much discussion regarding appropriate therapeutic monitoring of vancomycin in adult patients with significant S. aureus infections especially for those with higher vancomycin MICs. A recent consensus review of the American Society of Health-System Pharmacists, the Infectious Diseases Society of America, and the Society of Infectious Diseases Pharmacists addresses this problem.
The consensus review suggests minimum serum vancomycin trough concentrations should always be maintained above 10 mg/L to avoid development of resistance. However, for a pathogen with an MIC of 1 mg/L (vancomycin-susceptible), the minimum trough concentration should be at least 15 mg/L to generate the target AUC:MIC of 400. And in patients with normal renal function, the targeted AUC:MIC of >400 is not achievable with conventional dosing methods if the MIC is 2 mg/L (vancomycin-susceptible) or above (vancomycin-intermediate or -resistant), so alternate therapies should be considered.
Many clinical laboratories report susceptibility testing results with interpretive categories as opposed to MICs. These reports would not allow treating teams to tailor vancomycin treatment according to these new recommendations. Laboratories should consider reporting vancomycin MICs when testing S. aureus so that treating teams can determine the optimal dosing for vancomycin following the recent consensus guidelines.
- Clinical Laboratory Standards Institute 2009. Performance Standards for Antimicrobial Susceptibility Testing; Nineteenth Informational Supplement. CLSI document M100-S19. Clinical and Laboratory Standards Institute, Wayne, Pennsylvania.
- Rybak M et al. Therapeutic monitoring of vancomycin in adult patients: A consensus review of the American Society of Health-System Pharmacists, the Infectious Diseases Society of America, and the Society of Infectious Diseases Pharmacists. Am J Health-Syst Pharm. 2009; 66:82-98.
