Comparative Efficacies of Human Simulated Exposures of Tedizolid and Linezolid against Staphylococcus aureus in the Murine Thigh Infection Model

Tedizolid (formally torezolid) is an expanded-spectrum oxazolidinone with enhancedin vitro potency against Gram-positive pathogens, including methicillin-susceptibleStaphylococcus aureus (MSSA) and methicillin-resistantS. aureus (MRSA). The efficacies of human simulated exposures of tedizolid and linezolid againstS. aureus in an immunocompetent mouse thigh model over 3 days were compared. Four strains of MRSA and one of MSSA with tedizolid and linezolid MICs ranging from 0.25 to 0.5 and from 2 to 4 μg/ml, respectively, were utilized. Tedizolid or linezolid was administered in a regimen simulating a human steady-state 24-h area under the free concentration-time curve of 200 mg every 24 h (Q24) or 600 mg Q12, respectively. Thighs were harvested after 4, 8, 12, 24, 36, 48, and 72 h, and efficacy was determined by the change in bacterial density. The mean bacterial density in control mice increased over the 3-day period. After 24 h of treatment, a reduction in bacterial density of ≥1 log CFU was observed for both the tedizolid and linezolid treatments. Antibacterial activity was enhanced for both agents with a reduction of ≥2.6 log CFU after 72 h of treatment. Any statistically significant differences (P ≤ 0.05) in efficacy between the agents were transient and did not persist throughout the 72-h treatment period. The tedizolid and linezolid regimens demonstrated similarin vivo efficacies against theS. aureus isolates tested. Both agents were bacteriostatic at 24 h and bactericidal on the third day of treatment. These data support the clinical utility of tedizolid for skin and skin structure infections caused byS. aureus , as well as the bactericidal activity of the oxazolidinones after 3 days of treatment.