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 methodusing 7H11 medium. The MIC90 values of Y-26611 were as follows: Mycobacteriumtuberculosis (25 strains), 0.4, μg/ml; M. kansasii (19 strains), 6.25, μg/ml; M. marinum (10strains), 25, μg/ml; M. scrofulaceum (19 strains), 50μg/ml; M. avium (18 strains), 50μ g/ml; M. intracellulare (31 strains), >100, μg/ml; M. fortuitum (20 strains), 0.4, μg/ml; M. chelonae subsp. abscessus (15 strains), >100, μg/ml; and M. chelonae subsp. chelonae (20 strains), 100 μg/ml. The MICs against M. tuberculosis and M. fortuitum were lowerthan those of ofloxacin (OFLX), although it had somewhat higher MICs against M. aviumcomplex than OFLX. Antimicrobial activity of Y-26611 against M. tuberculosisphagocytosed in cultured murine peritoneal macrophages were somewhat lower, as comparedto that of OFLX. When M. fortuitum-infected (iv) A/J mice were treated with Y-26611 bygavage at doses of 0.5-2 mg/mouse, once daily, six times per week, from day 1 for up to 4weeks after infection, mice were protected from death and the number of CFU recoveredfrom their visceral organs, such as the lungs, spleen and kidneys were reduced. Thetherapeutic efficacy of Y-26611 was similar as that of OFLX.
