Evaluation of Ceftaroline Activity versus Daptomycin (DAP) against DAP-Nonsusceptible Methicillin-Resistant Staphylococcus aureus Strains in an In Vitro Pharmacokinetic/Pharmacodynamic Model

Abstract

ABSTRACT The objective of this study was to investigate the potential role of ceftaroline, a new broad-spectrum cephalosporin, as a therapeutic option for the treatment of daptomycin-nonsusceptible (DNS) methicillin-resistant Staphylococcus aureus (MRSA) infections. Four clinical DNS MRSA strains, R5717, R5563, R5996 (heteroresistant vancomycin-intermediate S. aureus ) and R5995 (vancomycin-intermediate S. aureus ) were evaluated in a two-compartment hollow-fiber in vitro pharmacokinetic/pharmacodynamic model at a starting inoculum of 10 7 CFU/ml for 96 h. Simulated regimens were ceftaroline at 600 mg every 12 h (q12h) (maximum free-drug concentration [ f C max ], 15.2 μg/ml; serum half-life [ t 1/2 ], 2.3 h), daptomycin at 6 mg/kg q24h ( f C max , 7.9 μg/ml; t 1/2 , 8 h), and daptomycin at 10 mg/kg q24h ( f C max , 15.2 μg/ml; t 1/2 , 8 h). Differences in CFU/ml between 24 and 96 h were evaluated by analysis of variance with Tukey's post-hoc test. Bactericidal activity was defined as a ≥3-log 10 CFU/ml decrease in the colony count from the initial inoculum. The ceftaroline MIC values were 0.25, 0.5, 0.5, and 0.5 μg/ml, and the daptomycin MIC values were 2, 2, 4, and 4 μg/ml for R5717, R5563, R5996, and R5995, respectively. Ceftaroline displayed sustained bactericidal activity against 3 of the 4 strains at 96 h (R5717, −3.1 log 10 CFU/ml; R5563, −2.5 log 10 CFU/ml; R5996, −5.77 log 10 CFU/ml; R5995, −6.38 log 10 CFU/ml). Regrowth occurred during the daptomycin at 6-mg/kg q24h regimen (4 strains) and the daptomycin at 10-mg/kg q24h regimen (3 strains). At 96 h, ceftaroline was significantly more active, resulting in CFU/ml counts lower than those obtained with daptomycin at 6 mg/kg q24h (4 strains, P ≤ 0.008) and daptomycin at 10 mg/kg q24 h (3 strains, P ≤ 0.001). Isolates with increased MIC values for daptomycin (all 4 strains) but not for ceftaroline were recovered. Ceftaroline was effective against the 4 isolates tested and may provide a clinical option for the treatment of DNS MRSA infections.