Background: Staphylococcus aureus is a major cause of bacteremia and is associated with high morbidity in adults and children. Daptomycin, a cyclic lipopeptide antibacterial agent, shows rapid in vitro bactericidal activity with concentration-dependent killing for Gram-positive organisms, including S. aureus. Clinical trials in adults demonstrated that daptomycin was safe and efficacious in complicated skin and skin structure infections and bacteremia caused by S. aureus, including right-sided infective endocarditis. However, information on the activity of daptomycin against Gram-positive isolates from children is lacking. The in vitro activities of daptomycin and comparator agents against S. aureus isolated from pediatric and adult patients with bacteremia, collected during 2012 and 2014, were assessed.
Methods: Non-duplicate, single patient bloodstream isolates of S. aureus (including methicillin-resistant [MRSA] and susceptible isolates) obtained via the Daptomycin Surveillance Program from United States (US) and Europe (EU) medical centers were tested for susceptibility (S) to daptomycin and comparator agents by broth microdilution per Clinical and Laboratory Standards Institute (CLSI) guidelines. CLSI and EUCAST breakpoints were used to determine %S, with data stratified by patient age (≤17 years [pediatric] and ≥18 years [adult]).
Results: S. aureus bloodstream isolates were collected from 494 US patients in 2012 and 1106 US/EU patients in 2014 (Table). MRSA comprised 43.7% of isolates in 2012 and 34.4% in 2014. According to CLSI breakpoints, daptomycin retained high activity levels between 2012 and 2014. Daptomycin was equally potent in pediatric isolates (100% S) compared with adult isolates (≥99.6% S) at both time points. Based on MIC50/90, daptomycin was two- to four-fold more potent than linezolid and vancomycin against bloodstream S. aureus isolates, irrespective of patient age or collection year.
Conclusion: Daptomycin demonstrated high in vitro activity against recent S. aureus bloodstream isolates. Daptomycin was equally potent against isolates from pediatric patients compared with adults, supporting the rationale for daptomycin treatment in pediatric subjects with bacteremia caused by S. aureus.
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