In vitro susceptibility of Mycobacterium avium complex to the new fluoroquinolone sparfloxacin (CI-978; AT-4140) and comparison with ciprofloxacin

We tested the activity of the new fluoroquinolone sparfloxacin (CI-978; AT 4140) against 30 strains of Mycobacterium avium complex (MAC) isolated from patients with acquired immune deficiency syndrome. MICs of sparfloxacin (range, less than or equal to 0.06 to 4 micrograms/ml) were lower than MICs of ciprofloxacin for all 30 strains, and MBCs for acid-fast bacteria were lower for 28 of the 30 strains. In synergism experiments using 10 strains of MAC, fractional inhibitory concentration indices revealed that the combination of sparfloxacin plus ethambutol was synergistic against 9 strains, and the three-drug combination of sparfloxacin plus ethambutol plus rifampin was synergistic against all strains. In the absence of ethambutol, the combination of sparfloxacin plus rifampin appeared to be antagonistic against three of the MAC strains.