Activity of ciprofloxacin and other fluorinated quinolones against mycobacteria.

The new fluorinated quinolones display interesting but variable activity against mycobacteria. Almost all compounds tested (ciprofloxacin, ofloxacin, enoxacin, norfloxacin, difloxacin, CI-934, A-56620, and megalone) inhibit Mycobacterium tuberculosis at achievable serum concentrations, with ciprofloxacin and ofloxacin most active by weight (minimal inhibitory concentration at which growth of 90 percent of strains is inhibited is equal to 1 microgram/ml or less). The growth of Mycobacterium kansasii, Mycobacterium xenopi, and Mycobacterium fortuitum is also well inhibited by these agents in the same range of concentrations. Activity against the Mycobacterium avium complex is method-dependent, with growth of perhaps one third of the strains isolated from patients with the acquired immune deficiency syndrome inhibited by ciprofloxacin. Determination of individual drug efficacy data in experimental mycobacterial infections is not a practical goal. However, combination therapy studies are in progress using murine models of both M. tuberculosis and M. avium challenges. Ofloxacin has been used with some success in human patients with pulmonary tuberculosis. Oral administration may be an important advantage, and, when used in combination with other active agents, the new quinolones may have a useful role in treating mycobacterial infections.