Vancomycin-resistant enterococcal bacteraemia and daptomycin: are higher doses necessary?.
King, Esther A. 1,*; McCoy, Dorothy 1,2; Desai, Samit 3; Nyirenda, Themba 4; Bicking, Keri 1
[Article]
Journal of Antimicrobial Chemotherapy.
66(9):2112-2118, September 2011.
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Background: The MIC corresponding to daptomycin susceptibility for vancomycin-resistant enterococci (VRE) is <=4 mg/L. Based on the concentration-dependent killing properties of daptomycin, there may be concern about achieving adequate concentrations when the MIC approaches the upper end of the susceptible range (3-4 mg/L). Higher doses of daptomycin may be needed to treat VRE isolates with higher MICs.
Methods: We conducted a single-centre retrospective chart review of adult cases with VRE bacteraemia who received daptomycin as initial therapy. The primary outcome was time to microbiological cure (TMC) between standard doses (<=6 mg/kg) and high doses (>6 mg/kg) of daptomycin and whether TMC differed based on MICs. The secondary outcome evaluated the daptomycin MIC distribution and assessed whether recent exposure to vancomycin was associated with higher daptomycin MICs.
Results: Forty-six cases were included in the primary analysis and 60.9% of patients were neutropenic. The two dose groups differed in the baseline characteristics of age, body mass index, blood culture source and catheter removal. Median TMC was 2 days for both dose groups. There was no significant difference in TMC between MIC subgroups of <=2 mg/L versus >2 and <=4 mg/L. For the secondary analysis 227 VRE isolates were evaluated and 62% had daptomycin MICs of 3-4 mg/L. Each daptomycin MIC group had a similar incidence of prior vancomycin exposure.
Conclusions: Based on this retrospective review we did not observe a difference in TMC based on daptomycin dose and MIC; however, there were various limitations to this study, and the study was not powered to detect a difference in TMC. Also, prior vancomycin exposure did not appear to influence daptomycin MICs. The frequency of daptomycin MICs of 3-4 mg/L reported in this study is higher than those reported in the literature.
(C) British Society for Antimicrobial Chemotherapy 2011. Published by Oxford University Press. All rights reserved.