Pazufloxacin (T-3761) mesylate is a fluoroquinolone antibiotic. Target: Antibacterial Pazufloxacin (T-3761), a new quinolone derivative, showed broad and potent antibacterial activity. T-3761 showed good efficacy in mice against systemic, pulmonary, and urinary tract infections with gram-positive and gram-negative bacteria, including quinolone-resistant Serratia marcescens and Pseudomonas aeruginosa. The in vivo activity of T-3761 was comparable to or greater than those of ofloxacin, ciprofloxacin, norfloxacin, and tosufloxacin against most infection models in mice. The activities of T-3761 were lower than those of tosufloxacin against gram-positive bacterial systemic and pulmonary infections in mice but not against infections with methicillin-resistant Staphylococcus aureus [1]. T-3761 had a broad spectrum of activity and had potent activity against gram-positive and -negative bacteria. The MICs of T-3761 against 90% of the methicillin-susceptible Staphylococcus aureus, methicillin-susceptible and -resistant Staphylococcus epidermidis, and Clostridium spp. tested were 0.39 to 6.25 micrograms/ml. The MBCs of T-3761 were either equal to or twofold greater than the MICs. The 50% inhibitory concentrations of T-3761 for DNA gyrases isolated from E. coli and P. aeruginosa were 0.88 and 1.9 micrograms/ml, respectively [2].