Effect of Coadministration of Moxifloxacin and Rifampin on Mycobacterium tuberculosis in a Murine Aerosol Infection Model

Coadministration of moxifloxacin and rifampin was evaluated in a murine model of Mycobacterium tuberculosis pulmonary infection to determine whether the finding of antagonism documented in a hollow-fiber infection model could be recapitulated in vivo. Colony counts were followed in a no-treatment control group, groups administered moxifloxacin or rifampin monotherapy, and a group administered a combination of the two agents. Following 18 days of once-daily oral administration to mice infected with M. tuberculosis, there was a reduction in the plasma exposure to rifampin that decreased further when rifampin was coadministered with moxifloxacin. Pharmacodynamic analysis demonstrated a mild antagonistic interaction between moxifloxacin and rifampin with respect to cell kill in the mouse model for tuberculosis (TB). No emergence of resistance was noted over 28 days of therapy, even with monotherapy. This was true even though one of the agents in the combination (moxifloxacin) induces error-prone replication. The previously noted antagonism with respect to cell kill shown in the hollow-fiber infection model was recapitulated in the murine TB lung model, although to a lesser extent.