Bacteriostatic and bactericidal activity of ciprofloxacin and ofloxacin against Mycobacterium tuberculosis and Mycobacterium avium complex.

MICs of ciprofloxacin were lower than MICs of ofloxacin for both M. tuberculosis and M. avium complex strains. The MICs of both drugs for 41 M. tuberculosis strains were in a narrow range, and significantly lower than the achievable serum concentrations. The MICs of ciprofloxacin for 46 M. avium strains were in a wide range, and in only 28% were the broth-determined MICs of ciprofloxacin within the same range as for M. tuberculosis and lower than the achievable serum level. When compared with the concentrations achievable in macrophages, the broth-determined MICs of ciprofloxacin were lower than this level for 61% of M. avium strains. Both drugs were bactericidal against M. tuberculosis and M. avium, with a low MIC/MBC ratio.