Moxifloxacin exhibits therapeutic activity against Mycobacterium avium infection in mice. Since not only moxifloxacin but also another 8-methoxy quinolone, gatifloxacin, and a C-8-chloro quinolone, sitafloxacin, show favourable antimycobacterial activity in vitro, their anti-M. avium activities were compared in vivo. Minimum inhibitory concentrations (MICs), minimum bactericidal concentrations (MBCs) and mutant prevention concentrations (MPCs) of the test quinolones for M. avium were determined by microdilution in 7HSF broth. Antimicrobial activity against intracellular bacteria was measured using Mono Mac 6 human macrophages. Therapeutic efficacy of the quinolones when administered subcutaneously with or without clarithromycin plus ethambutol was assessed using mice intravenously infected with M. avium in terms of changes in bacterial loads in the lungs and spleen following infection. Based on the MICs, MBCs and MPCs, the in vitro activities of sitafloxacin and moxifloxacin were greater than that of gatifloxacin. Moxifloxacin exhibited the strongest activity against intramacrophage M. avium. When each test quinolone was administered alone to infected mice, sitafloxacin and gatifloxacin exhibited greater therapeutic efficacy than moxifloxacin based on intrapulmonary bacterial elimination. However, moxifloxacin exerted greater activity in killing bacteria in the spleen. Moxifloxacin and sitafloxacin exhibited combined effects on intrapulmonary bacterial elimination when administered to mice in combination with clarithromycin plus ethambutol. Sitafloxacin exerted the most marked combined effects in bacterial killing in the spleen. Levofloxacin displayed the lowest in vitro and in vivo activities amongst the tested quinolones. Taken together, these findings indicate that sitafloxacin and moxifloxacin exhibit favourable activities against M. avium in vitro and in vivo.
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