Mutant prevention concentrations of daptomycin for Enterococcus faecium clinical isolates

Area of Science:

• Microbiology
• Pharmacology
• Infectious Diseases

Background:

• Vancomycin-resistant Enterococcus faecium (VRE) presents significant treatment challenges.
• Emergence of daptomycin resistance during therapy is increasingly reported.
• Understanding the mutant selection window (MSW) is crucial for optimizing antibiotic efficacy.

Purpose of the Study:

• To determine the mutant prevention concentrations (MPCs) and mutant selection windows (MSWs) for daptomycin against E. faecium.
• To perform a pharmacodynamic analysis of daptomycin's unbound Cmax in relation to MSW.

Main Methods:

• Determined minimum inhibitory concentrations (MICs) and MPCs using broth microdilution and agar dilution.
• Calculated MSWs (MPC/MIC ratio).
• Analyzed mean maximum plasma concentrations (Cmax) and unbound fractions at various dosages (4-12 mg/kg).

Main Results:

• Daptomycin MICs ranged from 0.5-4 mg/L; MPCs ranged from 2-32 mg/L.
• MSW wideness varied from 2x to 32x MIC.
• Unbound daptomycin Cmax fell within the MSW for 67-92% of strains at 4-6 mg/kg, and above MPC for most strains only at 12 mg/kg.

Conclusions:

• Free daptomycin Cmax typically falls within the MSW at lower dosages (<10 mg/kg), potentially facilitating resistance.
• Higher daptomycin dosages may be necessary to consistently exceed the MPC and prevent resistance.
• Further research is needed to optimize daptomycin dosing strategies for VRE infections.