Editorial Commentary: Early High-Dose Daptomycin for Methicillin-Resistant Staphylococcus aureus Bloodstream Infections With Elevated Vancomycin Minimum Inhibitory Concentrations: Ready for Prime Time?

Abstract

In this issue of Clinical Infectious Diseases, Murray and colleagues present results from a matched cohort study addressing the clinical conundrum of methicillinresistant Staphylococcus aureus (MRSA) bloodstream infections caused by organisms with elevated vancomycin minimum inhibitory concentrations (MICs) [1]. The investigators conclude that highdose daptomycin treatment led to better outcomes, and they advocate for an early switch from vancomycin to daptomycin based on finding a vancomycin MIC >1 μg/mL. Although the study provides new insight into this important clinical problem, several key questions remain. A growing body of data shows that S. aureus isolates with higher vancomycin MICs are associated with a significant increase in the risk of worse clinical outcomes, including treatment failure and death [2, 3]. It is unknown whether these poor outcomes represent relative resistance to vancomycin, a marker for a more virulent organism, or some undefined third factor associated with worse outcomes. Holmes et al found that the association between higher vancomycin MICs and clinical failure persisted even in patients with methicillin-susceptible S. aureus treated with β-lactam therapy [4]. This makes the decision regarding treatment of patients with MRSA bloodstream infection with an elevated vancomycin MIC even less clear. Should they be switched to an alternative therapy early, based on MIC testing, or wait until they develop persistent bloodstream infection or other signs of clinical failure? Current guidelines from the Infectious Diseases Society of America recommend higher doses of vancomycin based largely on pharmacokinetic and pharmacodynamic data and suggest that “if the patient has