Bactericidal activity of daptomycin, vancomycin, teicoplanin and linezolid against Staphylococcus aureus, Enterococcus faecalis and Enterococcus faecium using human peak free serum drug concentrations

The bactericidal activities of daptomycin, vancomycin, teicoplanin and linezolid at human peak free serum concentrations (Cmax,free) were determined against Staphylococcus aureus (one methicillin-susceptible and two methicillin-resistant strains), Enterococcus faecalis and Enterococcus faecium (one vancomycin-susceptible and one vancomycin-resistant strain of each). Daptomycin was rapidly bactericidal against 7/7 strains at Cmax,free of 22.0 mg/L (corresponding to 63% protein binding) and against 3/7 strains at 4.8 mg/L (corresponding to 92% protein binding). Vancomycin (18.0 mg/L) was bactericidal against only two strains. Both teicoplanin (4.5 mg/L) and linezolid (10.4 mg/L) were consistently bacteriostatic. Daptomycin is a useful option for the treatment of Gram-positive infections owing to its strong bactericidal activity.