Description_x000D_ Biochem/physiol Actions_x000D_ Sitafloxacin (DU-6859 or DU-6859a) is an orally active, fourth generation fluoroquinolone that exhibits broad-spectrum antibiotic activity against many Gram-positive, Gram-negative and anaerobic clinical isolates, including strains resistant to other fluoroquinolones, via dual inhibitory activity against bacterial DNA gyrase and topoisomerase IV (IC50 = 1.16 and 1.88 μg/mL against S. pneumoniae gyrA/B and parC/E, respectively). Sitafloxacin is active against methicillin-resistant staphylococci, Streptococcus pneumoniae and other streptococci with reduced susceptibility to levofloxacin and other quinolones and enterococci. Sitafloxacin also exhibits activity against clinical isolates of Klebsiella pneumoniae, Enterobacter cloacae, Pseudomonas aeruginosa as well as some activity against quinolone-resistant strains and Acinetobacter baumannii. Sitafloxacin in vitro activity against anaerobes is comparable to imipenem and metronidazole.