Susceptibility relationship between vancomycin and daptomycin in Staphylococcus aureus: facts and assumptions

The decrease in vancomycin treatment efficacy that is accompanying increases in vancomycin minimum inhibitory concentration (MIC) within the susceptible range (so-called MIC creep) has led to the suggestion that vancomycin is losing its potency in treating serious Staphylococcus aureus infections. Understanding the clinical importance of the microbiological effects of glycopeptides on bacterial lipopeptides and lipoglycopeptides will be crucial in treating serious meticillin-resistant S aureus infections. We review the observed effects of reduced glycopeptide susceptibility on the activities of daptomycin in S aureus in vitro and in vivo. Factors associated with loss of susceptibility and ways to reduce the risk of resistance to daptomycin are reviewed, including the importance of prompt mechanical reduction of bacterial inoculum through surgery or through potent or combination antibiotic therapy, as well as optimisation of daptomycin pharmacodynamic exposure.