Objectives: Daptomycin has shown clinical efficacy in diabetic foot infections (DFI). However, only limited data are available on its bone penetration in this particular population. The aim of this study was to determine daptomycin bone concentrations in patients with DFI undergoing surgery after multiple daptomycin infusions and to determine bone daptomycin inhibitory quotients (IQs) for the predominant gram-positive species involved in DFI.
Methods: Fourteen adult patients hospitalized with DFI treated with daptomycin and requiring surgical bone debridement and amputation were included in this single-centre prospective study. Daptomycin concentrations in serum and bone were determined by HPLC at steady state. Bone IQs were then calculated according to different minimum inhibitory concentrations (MICs; range 0.25-4mg/l) that are representative of the main MICs for Staphylococcus aureus, coagulase-negative staphylococci (CoNS), and Enterococcus sp populations.
Results: Residual and peak concentrations varied from 4.5mg/l to 39.9mg/l and from 31.8mg/l to 110.9mg/l, respectively. Bone daptomycin concentrations at the moment of surgery varied from 1.2mg/l to 17mg/l. Up to a MIC of 1mg/l, which is the epidemiological cut-off value (ECOFF) and breakpoint value for S. aureus and CoNS, all bone daptomycin IQs were positive. The highest bone IQs were observed with Staphylococcus species. Calculated bone IQs for Enterococcus species were often weak at MIC values near the ECOFF.
Conclusions: Daptomycin penetrates bone well in patients treated for DFI. At an initially recommended dosage of 6mg/kg, bone concentrations are likely to be effective against staphylococcal infections and infections due to low-MIC Enterococcus.
Keywords: Bacterial foot infection; Bone concentration; Daptomycin.
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