In vitro PK/PD model.

Strains were inoculated into TSA plates incubated at 37°C for 24 h and then suspended in normal saline to reach a concentration equivalent to a 0.5 McFarland standard. The in vitro model consisted of a previously described CDC biofilm reactor (CBR) model (BioSurface Technologies, Bozeman, MT) that was set up with polyurethane coupons inserted into eight rods, with flow rates simulating human PK, to evaluate the in vitro activities of antimicrobials (28, 36). Briefly, a 40-h biofilm conditioning phase was performed prior to an evaluation of the antimicrobials and consisted of 24 h of incubation at 37°C of inoculated 1% gSTSB, followed by 16 h of continuous flow with a 1/10 concentration of gSTSB carried out with peristaltic pumps (Masterflex; Cole-Parmer Instrument Co., Chicago, IL, USA). After the completion of the conditioning and continuous-flow phases, Mueller-Hinton broth supplemented with albumin was utilized as the medium for the model experiments. Boluses of antimicrobials were injected into the reactor after the biofilm conditioning phase was completed. Each CBR model allowed for 8 rods with 2 polyurethane coupons each. The CBR was placed in a 37°C walk-in incubator throughout the procedure. Fresh medium was continuously supplied and removed from the model along with the drug via a peristaltic pump set to simulate the half-life of the drugs. Supplemental telavancin was added at an appropriate rate to ceftaroline or rifampin combination models to compensate for the higher flow rate required to simulate ceftaroline and rifampin clearance. The regimens evaluated were telavancin 7.5 mg/kg q24h (peak drug concentrations [C_max], 87.5 mg/liter; t_1/2, 8.1 h; protein binding, 90%), telavancin 10 mg/kg q24h (C_max, 108 mg/liter; t_1/2, 8.1 h; protein binding, 90%) (37), ceftaroline 600 mg q8h (C_max, 21.3 mg/liter; t_1/2, 2.66 h; protein binding, 20%) (38), rifampin 450 mg q12h (C_max, 10.54 mg/liter; t_1/2, 3 h; protein binding, 80%) (39), telavancin 7.5 mg/kg q24h plus ceftaroline 600 mg q8h, telavancin 7.5 mg/kg q24h plus rifampin 450 mg q12h, telavancin 10 mg/kg q24h plus ceftaroline 600 mg q8h, telavancin 10 mg/kg q24h plus rifampin 450 mg q12h, and a growth control. All model experiments were completed in duplicate to ensure reproducibility.