Susceptibility of Mycobacterium tuberculosis strains to Gatifloxacin and Moxifloxacin by different methods.

Chemotherapy; 2006; 52; 190-195.

Abstract: Background: Considering the potentials of gatifloxacin and moxifloxacin in the treatment of tuberculosis, the present study was aimed to define resistance to both these drugs.

Methods: Fifty Mycobacterium tuberculosis isolates, consisting of 30 ofloxacin-susceptible and 20 ofloxacin-resistant strains, were tested for their susceptibility to gatifloxacin and moxifloxacin using different susceptibility testing methods, namely the absolute concentration method on Lowenstein-Jensen medium (LJ), the proportion susceptibility testing method (PST) on LJ and 7H11 agar media, and the BACTEC radiometric method.

Result: The minimal inhibitory concentration (MIC) of gatifloxacin and moxifloxacin was 1 µg/ml by the absolute concentration method on LJ. In the PST method on LJ and 7H11, using a criterion of 1% growth as resistant, there was 100% agreement with the absolute concentration method at a concentration of 0.5 µg/ml for gatifloxacin, and 96% agreement with the BACTEC method at a concentration of 0.25 µg/ml. For moxifloxacin, results by the PST method showed 96% agreement with the absolute concentration method on LJ at a concentration of 1 µg/ml and 92% agreement at a concentration of 0.5 µg/ml for both the absolute concentration method on 7H11 and the BACTEC method.

Conclusions : The MICs of gatifloxacin and moxifloxacin were much lower than the MICs of other quinolones like ofloxacin and ciprofloxacin. Additionally, these two drugs have shown a low mean MIC and low concentration as a definition of resistance, which might help in treating the patients with low levels of quinolone resistance.

Keywords : Mycobacterium tuberculosis ?Gatifloxacin ?Moxifloxacin

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