Comparative antimycobacterial activities of ofloxacin, ciprofloxacin and grepafloxacin.

Infections caused by non-tuberculous mycobacteria and multidrug-resistant Mycobacterium tuberculosis are difficult to treat. New compounds potentially active against these bacteria are therefore constantly being sought. Among them is grepafloxacin, a new C5 fluoroquinolone. A panel of 130 isolates of mycobacteria including 33 M. tuberculosis isolates and 97 isolates of different species of atypical mycobacteria were analysed for susceptibility to grepafloxacin, ofloxacin and ciprofloxacin. The MICs of these fluoroquinolones were determined using the agar-dilution method. Different mycobacterial species showed different degrees of susceptibility to grepafloxacin, ofloxacin and ciprofloxacin but little difference was observed between the MICs of the three antibiotics against strains of the same mycobacterial species. In addition, to evaluate the intracellular activity of these drugs, six strains of mycobacteria were studied using a human-macrophage infection model. Preliminary results of macrophage experiments showed that grepafloxacin was more active than ofloxacin and ciprofloxacin, particularly against Mycobacterium kansasii and, to a lesser degree, against Mycobacterium avium complex and Mycobacterium marinum. However, the three fluoroquinolones had comparable activities against M. tuberculosis.