Retrospective Observational Study Comparing Vancomycin Versus Daptomycin as Initial Therapy for Staphylococcus aureus Infections

BackgroundData comparing alternatives to vancomycin for the treatment of Staphylococcus aureus infections with vancomycin MIC >1 are lacking.ObjectiveWe evaluated outcomes of S aureus infections based on whether daptomycin or vancomycin was used as initial therapy at a single institution, where the majority of S aureus infections had vancomycin MICs of 2 mg/L.MethodsA retrospective chart review was conducted at a 450-bed private acute care hospital. All patients >18 years of age who received initial vancomycin or daptomycin for at least 3 days to treat an S aureus infection between November 2006 and July 2008 were included. Patients with endocarditis, osteomyelitis, or a central nervous system infection and/or those being treated for an S aureus respiratory tract infection were excluded.ResultsA total of 165 patients (median age 68 years, range 24–95 years; 56% male) were included: 57 (35%) received daptomycin and 108 (65%) received vancomycin; 78% had vancomycin MIC values of 2 mg/L. The median antibiotic-related length of stay was significantly shorter with daptomycin than with vancomycin (7.5 vs 10.0 days; P = 0.035). Relapse rates in the clinically evaluable population were 25% and 23% for daptomycin and vancomycin, respectively; for the subset with S aureus bacteremia with vancomycin MICs of 2 mg/L, rates were 0% (0/9 patients) and 26% (6/23 patients) for daptomycin and vancomycin, respectively (P = 0.089). Thirty-day all-cause mortality was 6% (10/165 patients) and did not differ significantly by treatment: 7% (4/57 patients) versus 6% (6/108 patients) for daptomycin and vancomycin, respectively (P = 0.708).ConclusionIn this setting, in which the majority of S aureus infections had vancomycin MIC values of 2 mg/L, we found the median antibiotic-related length of stay to be significantly shorter with daptomycin than with vancomycin. Prospective studies are needed to determine whether daptomycin confers benefits over vancomycin in specific infection types under conditions that are unfavorable for vancomycin, such as higher vancomycin MICs.