Bactericidal activity of moxifloxacin on exponential and stationary phase cultures of Mycobacterium tuberculosis.

The bactericidal activity of moxifloxacin, alone and in combination with isoniazid and rifampin, was studied on exponential and stationary phase cultures of Mycobacterium tuberculosis H37 Rv strain, the standard strain which is a wild type of M. tuberculosis strain, not exposed to any environment, susceptible to all anti-tuberculosis drugs. Moxifloxacin alone was highly bactericidal, being intermediate in activity between isoniazid and rifampin on both types of culture. The speed of activity was slow with the stationary phase culture, causing a reduction from 6.41 log(10) cfu/ml to 2.70 log(10) cfu/ml on day 6 with the higher moxifloxacin concentration of 4 mu g/ml and to 4.08 log(10) cfu/ml with the lower concentration of 0.25 mu g/ml. When added to isoniazid, its activity against both exponential and stationary phase cultures was increased. However, when it was added to rifampin, no increase in activity was found with either type of culture. Addition of moxifloxacin to isoniazid and rifampin resulted in a slight increase in activity against the exponential culture but a considerable increase against the stationary culture with counts below the limit of detection at 4 and 6 days with both moxifloxacin concentrations. The synergism found with isoniazid, but not with rifampin, supports the view that isoniazid should be included in combinations with moxifloxacin during the therapy of pulmonary tuberculosis.