[Antimycobacterial activity of a newly synthesized fluoroquinolone, Y-26611]

Y-26611, a newly developed fluoroquinolone having a morpholine moiety at the 7 position was examined for in vitro antimycobacterial activity by the agar dilution method using 7H11 medium. The MIC90 values of Y-26611 were as follows: Mycobacterium tuberculosis (25 strains), 0.4 micrograms/ml; M. kansasii (19 strains), 6.25 micrograms/ml; M. marinum (10 strains), 25 micrograms/ml; M. scrofulaceum (19 strains), 50 micrograms/ml; M. avium (18 strains), 50 micrograms/ml; M. intracellulare (31 strains), greater than 100 micrograms/ml; M. fortuitum (20 strains), 0.4 micrograms/ml; M. chelonae subsp. abscessus (15 strains), greater than 100 micrograms/ml; and M. chelonae subsp. chelonae (20 strains), 100 micrograms/ml. The MICs against M. tuberculosis and M. fortuitum were lower than those of ofloxacin (OFLX), although it had somewhat higher MICs against M. avium complex than OFLX. Antimicrobial activity of Y-26611 against M. tuberculosis phagocytosed in cultured murine peritoneal macrophages were somewhat lower, as compared to that of OFLX. When M. fortuitum-infected (iv) A/J mice were treated with Y-26611 by gavage at doses of 0.5-2 mg/mouse, once daily, six times per week, from day 1 for up to 4 weeks after infection, mice were protected from death and the number of CFU recovered from their visceral organs, such as the lungs, spleen and kidneys were reduced. The therapeutic efficacy of Y-26611 was similar as that of OFLX.