Comparative in-vitro activity of fleroxacin and other 6-fluoroquinolones against mycobacteria.

The susceptibility of 11 clinical isolates of Mycobacterium tuberculosis, 3 M. kansasii, 3 M. xenopi, 2 M. scrofulaceum, 2 M. marinum, 2 M. malmoense to fleroxacin, ciprofloxacin, norfloxacin, rifampicin, isoniazid, ethambutol, and streptomycin was determined by the standard proportion method (Middlebrook 7H10 agar). All M. tuberculosis, M. kansasii, M. xenopi, M. scrofulaceum, M. marinum, and M, malmoense isolates including those resistant to conventional antimycobacterials were inhibited by 0.5 mg/l of fleroxacin and ciprofloxacin, the lowest tested concentration. Fleroxacin and ciprofloxacin along with ofloxacin, pefloxacin, ansamycin, clofazimine and cycloserine were also tested against 14 isolates of the M. avium complex. Nine of 14 strains (64%) of the M. avium complex were found susceptible to 4 mg/l of fleroxacin and a similar percentage to the other quinolones. On the basis of its in-vitro potency and its favourable pharmacokinetic properties fleroxacin appears to be sufficiently active to warrant further experimental trials against difficult to treat mycobacteria.