Time-kill curves of daptomycin and Monte Carlo simulation for the treatment of bacteraemia caused by Enterococcus faecium.

Objectives: The aim of this study was to investigate the effect of daptomycin against vancomycin-resistant Enterococcus faecium bacteraemia using computer modelling.
Methods: Data obtained in vitro from time-kill curves were evaluated by PK/PD modelling and Monte Carlo simulations to determine the logarithmic reduction in the number of colony-forming units (CFU)/mL over 18 days of daptomycin treatment at 6, 8, and 10 mg/kg doses every 24 or 48 h and with variations in creatinine clearance (CL _CR ) of 15-29, 30-49, and 50-100 mL/min/1.73 m ² . Monte Carlo simulations were performed to evaluate the probability of target attainment (PTA) for an area under the unbound drug concentration-time curve/minimum inhibitory concentration (fAUC/MIC) > 36 at the same doses and CL _CR .
Results: Static time-kill model was employed to investigate the antibacterial efficacy of constant daptomycin concentrations. The time-kill curve analysis was performed using mathematical modelling based on a Hill coefficient factor. There was an expressive reduction (> 2 Log CFU/mL) over 18 days of daptomycin treatment in 75th percentile of individuals with CL _CR of 15-100 mL/min/1.73 m ² ) with daptomycin 6-10 mg/kg/day, except for daptomycin every 48 h. Using fAUC/MIC > 36, PTA was > 90% at MICs ≤ 2 μg/mL.
Conclusions: Higher daptomycin doses were associated with higher mortality in time-kill curves. The simulations indicated that independent of the CL _CR the therapeutic responses of VRE occur with doses of daptomycin ≥ 6 mg/kg/day and daptomycin every 48 h is insufficient to treat enterococcal bacteraemia.