Medical Research: What are the main findings of the study?
Dr. Kalil: In recent years, physicians treating staph infections with vancomycin have seen an increase in the minimum inhibitory concentration (MIC), the lowest concentration of an antimicrobial agent that inhibits the growth of a microorganism. This condition is referred to as vancomycin “MIC creep.” It is an indicator that the bacteria might be developing a reduced susceptibility to vancomycin. There also have been reports suggesting that elevations in vancomycin MIC values may be associated with increased treatment failure and death.
To determine the effectiveness of vancomycin and other newer antibiotics used to treat Staphylococcus aureus, the UNMC team analyzed nearly 8,300 episodes of Staphylococcus aureus bloodstream infections from patients around the U.S. and in several other countries. The adjusted absolute risk of mortality among patients with Staphylococcus aureus bloodstream infections with high-vancomycin MIC was not statistically different from patients with Staphylococcus aureus bloodstream infections with low-vancomycin MIC.
Medical Research: What was most surprising about the results?
Dr. Kalil: Even though vancomycin has been used for more than 50 years, it still remains highly effective against Staphylococcus aureus bloodstream infections.
Medical Research: What should clinicians and patients take away from your report?
- Standards for vancomycin MIC most likely do not need to be lowered;
- Routine differentiation of MIC values between 1mg/L and 2 mg/L appears unnecessary;
- The use of alternative antistaphylococcal agents may not be required for Staphylococcus aureus isolates with elevated but susceptible vancomycin MIC values.
Kalil AC, Van Schooneveld TC, Fey PD, Rupp ME. Association Between Vancomycin Minimum Inhibitory Concentration and Mortality Among Patients With Staphylococcus aureus Bloodstream Infections: A Systematic Review and Meta-analysis. JAMA. 2014;312(15):1552-1564. doi:10.1001/jama.2014.6364.