In vitro activities of levofloxacin used alone and in combination with first- and second-line antituberculous drugs against Mycobacterium tuberculosis

Abstract

By using the radiometric BACTEC 460-TB methodology, the inhibitory and bactericidal activity of the optically active L-isomer of ofloxacin (levofloxacin) was compared with those of the D-isomer and the commercially available mixture containing equal amounts of DL-isomers (ofloxacin) against the Mycobacterium tuberculosis complex (type strain H37Rv, a panel of drug- susceptible and -resistant clinical isolates including multidrug-resistant isolates of M. tuberculosis, as well as M. africanum, M. bovis, and M. bovis BCG). Levofloxacin MICs (range, 0.50 to 0.75 μg/ml) were about 1 dilution lower than those of ofloxacin (MIC range, 0.75 to 1.00 μg/ml) and 5 to 6 dilutions lower than those of the D-isomer (MIC range, 32 to 60 μg/ml). The MICs of levofloxacin, ofloxacin, and D-ofloxacin at which 90% of the strains are inhibited were 0.50, 1.00, and 64 μg/ml, respectively. The multidrug- resistant M. tuberculosis strains resistant to first-line drugs were as susceptible to quinolones as the wild-type drug-susceptible isolates. Levofloxacin at 0.5 μg/ml showed bactericidal activity comparable to the activities of 1.0 μg of ofloxacin per ml and 64 μg of D-ofloxacin per ml, with MBCs within the range of 0.5 to 2.0 μg/ml, compared with MBCs of 0.75 to 4.0 μg of ofloxacin per ml for M. tuberculosis, M. africanum, M. bovis, and M. bovis BCG. Combination testing of sub-MICs of levofloxacin with other first-line (isoniazid, rifampin, and ethambutol) and second-line (amikacin and clofazimine) antituberculous drugs was evaluated with various two-, three-, and four-drug combinations; enhanced drug activity was observed in 8 of 25, 12 of 20, and 8 of 15 tests, respectively, indicating that levofloxacin acts in synergy with other antituberculous drugs.