Correlates of therapeutic efficacy in experimental methicillin-resistant Staphylococcus aureus endocarditis

Seventy animals with experimental aortic valve endocarditis due to methicillin-resistant Staphylococcus aureus (MRSA) were randomized to receive: no therapy; pefloxacin 40 or 80 mg/kg/day i.v.; or vancomycin 30 mg/kg/day i.v. Vancomycin caused a more rapid decrease in intravegetation MRSA counts than pefloxacin at 40 or 80 mg/kg/day (p < 0.001, p < 0.05, respectively, therapy day 3). The major correlate of therapeutic efficacy in this study was the significantly higher mean intravegetation levels achieved by vancomycin (16.8 ± 6.1 μg/g) versus those attained by pefloxacin therapy at either 40 (1.6 ± 0.13 μg/g) or 80 mg/kg/day (2.8 ± 0.53 μg/g, p < 0.005, p < 0.025, respectively).