Is it time to replace vancomycin in the treatment of methicillin-resistant Staphylococcus aureus infections?

Abstract

For more than 4 decades, vancomycin has been the antibiotic of choice for methicillin-resistant Staphylococcus aureus (MRSA) infections. Recently, infections due to isolates with high but susceptible vancomycin minimum inhibitory concentrations have been associated with additional treatment failures and patient mortality. These poorer outcomes may in part be explained by the inability of attaining appropriate vancomycin levels in these patients. However, assumptions that these poor outcomes are solely due to failure to achieve optimal serum levels of vancomycin are premature. The availability of effective alternatives further erodes the position of vancomycin as first-line therapy. The emergence of resistance and cost considerations, however, favor a more measured approach when using alternative antimicrobials. Collectively, the current available data suggest that the optimal therapy for MRSA infections remains unclear. In the absence of further data, the Infectious Diseases Society of America guidelines remain relevant and inform clinicians of best practice for treating patients with MRSA infections.

Keywords: AUC/MIC targets; MRSA, hVISA, VISA; Staphylococcus aureus; minimum inhibitory concentration (MIC); vancomycin.

Figure 1.

Forest plot of all-cause 30-day mortality for Staphylococcus aureus infections stratified by high (≥1.5 mg/L) and low (<1.5 mg/L) vancomycin minimum inhibitory concentrations. Figure adapted from van Hal et al [10] with permission (Oxford University Press). Readers are encouraged to consult the meta-analysis for specific details of the original reviewed studies. Abbreviations: CI, confidence interval; M-H, Mantel-Haenszel; MIC, minimum inhibitory concentration.

Figure 2.

Performance of Etest and Vitek2 compared to broth microdilution for vancomycin minimum inhibitory concentration (MIC). Data adapted from van Hal et al [25] with permission (Oxford University Press). Test results are interpreted compared to broth microdilution as the gold standard. Of note, although the correlation between MIC results differs significantly between methodologies, both these assays perform adequately with respect to regulatory agencies as the overall agreement is >95% (ie, an accepted variance of ±1 dilution). Abbreviation: MIC, minimum inhibitory concentration.