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Study: elevated vancomycin MICs no cause for concern

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Ann Griswold, PhD

December 2014—Elevated vancomycin minimum inhibitory concentrations do not increase the risk of death in patients with Staphylococcus aureus bacteremia, according to the findings of a comprehensive meta-analysis published in the Oct. 9 issue of JAMA.

Despite widespread speculation about rising vancomycin resistance, or “MIC creep,” the authors find little evidence to challenge the current CLSI susceptibility breakpoint of ≤ 2 µg/mL for vancomycin.

Dr. Kalil

Dr. Kalil

“After an extensive approach and analysis, we found that MICs of one and two have pretty much similar mortality,” says coauthor Andre C. Kalil, MD, MPH, a professor of medicine in the Infectious Diseases Division of the University of Nebraska Medical Center. The results remained consistent across a variety of study designs, microbiological susceptibility assays, MIC cutoffs, clinical outcomes, durations of bacteremia, and histories of previous vancomycin exposure and treatment.

The findings may help boost clinicians’ confidence in vancomycin therapy and stave off opportunities for S. aureus to develop multidrug resistance, the authors note.

“Based on an MIC of two, some physicians might change the patient’s therapy to daptomycin because the literature essentially suggested there were vancomycin failures if the MIC was over one,” says coauthor Paul D. Fey, PhD, D(ABMM), a professor of pathology and microbiology at the University of Nebraska Medical Center and medical director of the clinical microbiology laboratory. Dr. Fey interpreted the susceptibility test results and contributed microbiology expertise to the study.

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