The combination of rifampin plus moxifloxacin is synergistic for suppression of resistance but antagonistic for cell kill of Mycobacterium tuberculosis as determined in a hollow-fiber infection model

Abstract

Moxifloxacin is under development for expanded use against Mycobacterium tuberculosis. Rifampin is a mainstay of therapy. We examined the interaction of moxifloxacin plus rifampin for log-phase and nonreplicating persister (NRP) organisms. For this evaluation, we employed our hollow-fiber infection model, in which organisms are exposed to clinically relevant drug concentration-time profiles and the impact on bacterial cell kill and resistant subpopulation amplification is determined. In log phase, resistance emergence was observed in all monotherapy regimens and in no combination therapy regimen. No difference was seen in time to a 3-log reduction in the bacterial burden; there was a significant difference in time to resistance emergence (P = 0.0006). In the NRP experiment, no resistance emergence was seen. There was a significant difference between the monotherapy and combination therapy regimens in time to a 3-log reduction in the bacterial burden (P = 0.042). The combination is efficacious for suppressing resistant organisms but is antagonistic for cell kill.

FIG 1

Effects of moxifloxacin alone and in combination on log-phase M. tuberculosis H37Ra. Panels: A, rifampin treatment; B, moxifloxacin treatment; C, 100 mg moxifloxacin in combination with three rifampin regimens; D, 200 mg moxifloxacin in combination with three rifampin regimens; E, 400 mg moxifloxacin in combination with three moxifloxacin regimens. Drug administrations were done once daily.

FIG 2

Emergence of resistance during drug administration. Panels: A, control; B, 300 mg rifampin QD; C, 600 mg rifampin QD; D, 200 mg moxifloxacin QD; E, 800 mg moxifloxacin QD; F, 200 mg moxifloxacin QD plus 100 mg rifampin QD.

FIG 3

Times to resistance emergence in M. tuberculosis H37Ra for single versus combination chemotherapy. The difference is significant (P = 0.0006; Breslow-Gahan test). Red is monotherapy arms. Blue is combination therapy arms.

FIG 4

Nile red staining of log-phase and NRP M. tuberculosis. (A) Organisms held in anaerobiosis for 28 days and thought to be in the Wayne-Hayes level II state. (Left) Organisms are visibly stained with Nile red. (Right) Organisms visualized by phase-contrast microscopy. (B) Organisms in log-phase growth. (Left) No staining visible with Nile red. (Right) Organisms visualized by phase-contrast microscopy.

FIG 5

Presence of 16-kDa α-crystalline protein, a proof of attainment of Wayne-Hayes level II anaerobiosis.

FIG 6

Effects of moxifloxacin alone and in combination on NRP-phase (Wayne-Hayes level II anaerobiosis) M. tuberculosis H37Ra. Panels: A, rifampin treatment; B, moxifloxacin treatment; C, 100 mg moxifloxacin in combination with three rifampin regimens; D, 200 mg moxifloxacin in combination with three rifampin regimens; E, 400 mg moxifloxacin in combination with three moxifloxacin regimens; F, effect of continuous infusion of isoniazid and continuous infusion of metronidazole. Drug administrations were done once daily.

FIG 7

Times to achievement of a 3-log kill of M. tuberculosis H37Ra cells in the NRP phase for single versus combination chemotherapy. The difference is significant (P = 0.042; Breslow-Gahan test). Red is monotherapy arms. Blue is combination therapy arms.