Notes from Dr. RW: Treating MRSA: will vancomycin let you down?.
How can you know? Look at the susceptability data. Higher MICs, even in the susceptability range, may warn of treatment failure. Here are some papers mentioned at SHM 2009: In MRSA bacteremia vancomycin MICs of 1.5 or greater were associated with a 36.4% treatment failure rate. This paper showed an atypically high failure rate in bacteremic patients regardless of the MIC, and a virtual guarantee of failure for MICs above 1. For MRSA isolates with vancomycin MICs less than 0.5 µg/ml, vancomycin was 55.6% successful in the treatment of bacteremia whereas vancomycin was only 9.5% effective in cases in which vancomycin MICs for MRSA were 1 to 2 µg/ml. This paper showed higher mortality in MRSA bacteremia treated with vancomycin when the MIC was above 1.
