A fluoroquinolone antibiotic; active against clinical isolates of a variety of Gram-positive and Gram-negative bacteria in vitro, including K. pneumoniae, H. influenzae, N. gonorrhoeae, P. mirabilis, S. pyogenes, and MRSA (MIC50s = 0.025-0.78 μg/ml); inhibits DNA gyrase from E. coli, P. aeruginosa, and S. aureus (IC50s = 0.47, 11.0, and 2.5 μg/ml, respectively, in a DNA supercoiling assay); reduces mortality in mouse models of systemic S. aureus, MRSA, S. pneumoniae, K. pneumoniae, and P. aeruginosa infection (ED50s = 5, 20, 10, 160, and 50.4 mg/kg, respectively)