The activity of several newer antimicrobials against logarithmically multiplying M. leprae in mice.

INTRODUCTION Moxifloxacin, rifampicin, rifapentine, linezolid, and PA 824, alone and in combination, have been previously administered, as single doses and five times daily doses, to M. leprae infected mice during lag phase multiplication and were each found to have some bactericidal activity. DESIGN The fluroquinolones, ofloxacin, moxifloxacin and gatifloxacin, (50 mg/kg, 150 mg/kg and 300 mg/kg) and the rifamycins (5 mg/kg, 10 mg/kg, and 20 mg/kg), rifampicin and rifapentine, were evaluated alone and in combination for bactericidal activity against M. leprae using the mouse footpad model during logarithmic multiplication. Linezolid and PA 824 were similarly evaluated alone and linezolid in combination with rifampicin, minocycline and ofloxacin. RESULTS The three fluroquinolones and rifamycins were found alone and in combination to be bactericidal at all dosage schedules. PA 824 had no activity against M. leprae, while linezolid at a dose of 25 mg/kg was bacteriostatic, and progressively more bactericidal at doses of 50 mg/kg and 100 mg/kg. No antagonisms were detected between any of these drugs when used in combinations. CONCLUSION Moxifloxacin, gatifloxacin, rifapentine and linezolid were found bactericidal against rapidly multiplying M. leprae.