NEW YORK (Reuters Health) – Outcomes of bloodstream infections due to methicillin-resistant Staphylococcus aureus (MRSA) with elevated vancomycin minimum inhibitory concentration (MICs) are better when treated with daptomycin rather than vancomycin, according to a report in Clinical Infectious Diseases online November 21.“These findings support the recommendations of recent guidelines, which suggest consideration of the switch to alternative agents when the isolate has a high vancomycin MIC or when patients are not improving during receipt of therapy,” the authors conclude.Dr. Marcus J. Zervos and colleagues with Wayne State University School of Medicine and Henry Ford Hospital in Detroit, Michigan, explain that while the breakpoint for susceptibility of MRSA to vancomycin is a MIC of 2 mcg/mL, there have been reports of treatment failure in bloodstream infections involving MRSA with MICs below this threshold. They note that recent guidelines recommend consideration of alternative agents for treating MRSA infections when the vancomycin MIC is >l mcg/mL, but supporting data for this approach are sparse. To investigate, the team conducted a retrospective study of patients hospitalized at their institution with a MRSA bloodstream infection with a MIC between 1 and 2 mcg/mL. A total of 59 patients treated with daptomycin were compared with 118 matched vancomycin-treated patients.Rates of treatment failure, defined as a composite of death, microbiologic failure or recurrence of infection, were 17% in the daptomycin group and 31% in the vancomycin group, they researchers found, although this difference was not statistically significant (p=0.084). The benefit was mainly driven by a lower mortality incidence with daptomycin (9%) than with vancomycin (20%; p=0.048), the report indicates. “The results of the present study provide the first clinical comparison of alternative therapy in patients with MRSA BSI (bloodstream infection) with a high vancomycin MIC and confirm that vancomycin-treated patients are at high risk for failure; however, this risk is mitigated by treatment with daptomycin,” Dr. Zervos and colleagues conclude.In an editorial, Drs. Adam Weston and Helen W. Boucher with Tufts University School of Medicine in Boston, Massachusetts, note that daptomycin treatment is less successful in patients with moderate renal impairment, and there are safety concerns with its use. Cost is another factor.These reasons, they write, “preclude our recommending daptomycin for all patients with elevated vancomycin MICs.”That said, they conclude, “We hope that future prospective studies will clarify the question of whether every patient with an elevated vancomycin MIC benefits from daptomycin therapy.”Daptomycin Versus Vancomycin for Bloodstream Infections Due to Methicillin-Resistant Staphylococcus aureus With a High Vancomycin Minimum Inhibitory Concentration: A Case-Control StudyClin Infect Dis 2011.