Activity of moxifloxacin by itself and in combination with ethambutol, rifabutin, and azithromycin in vitro and in vivo against Mycobacterium avium

Abstract

Moxifloxacin activity against Mycobacterium avium complex (MAC) was evaluated in vitro against 25 strains. The MIC was determined to range from 0.125 to 2.0 microg/ml. In addition, U937 macrophage monolayers infected with MAC strain 101 (serovar 1) were treated with moxifloxacin (0.25 to 8 microg/ml) daily, and the number of intracellular bacteria was quantitated after 4 days. Moxifloxacin showed inhibitory activity at 0.5 microg/ml and higher. To assess the activity of moxifloxacin containing regimens in vivo, we infected C57BL bg(+)/bg(+) mice with 3 x 10(7) MAC strain 101 bacteria intravenously. One week later treatment was begun with the following: (i) moxifloxacin (50 mg/kg/day or 100 mg/kg/day), ethambutol (100 mg/kg/day), or a combination of moxifloxacin and ethambutol; or (ii) moxifloxacin (100 mg/kg/day), azithromycin (200 mg/kg/day), or rifabutin (40 mg/kg/day) as oral monotherapy; or (iii) all permutations of two-drug therapy or all three drugs in combination. All groups contained at least 14 animals, and the control group received the drug vehicle. After 4 weeks, quantitative blood cultures were obtained and the number of bacteria in liver and spleen was quantitated. Moxifloxacin, ethambutol, and azithromycin were active as single agents in liver, spleen, and blood. Rifabutin showed inhibitory activity only in the blood. Two-drug combinations containing azithromycin were no more active than azithromycin alone. Similarly, the three-drug combination was not more active than azithromycin alone in the spleen. Rifabutin did not add to the activity of any other single agent or two-drug combination. Moxifloxacin at both concentrations in combination with ethambutol was significantly more active than each drug alone.

Figures

FIG. 1

Activity of moxifloxacin against the MAC 101 strain using the macrophage system, as described in Materials and Methods. Infected U937 macrophages were treated with moxifloxacin (at different concentrations) for 4 days. The experiment was repeated six times. The data represent the mean ± the standard deviation. Concentrations of ≥0.5 μg/ml to ≤1.0 μg/ml had a P value of 0.04 compared with the untreated control. For treatment with 2 μg/ml the P value was 0.03, and for the differences between 4 and 8 μg/ml and the control the P value was 0.01. Both 4 and 8 μg/ml of moxifloxacin were bactericidal in this system.

FIG. 2

(A) Activity of moxifloxacin (MXF) alone at 50 mg/kg in liver and spleen or in combination with ethambutol (EMB) at 100 mg/kg. Fourteen mice were used per group per time point. P was <0.05 when moxifloxacin at 50 mg/kg was compared to the control at the same time point in both liver and spleen. P was <0.05 when moxifloxacin plus ethambutol in both liver and spleen was compared with moxifloxacin or ethambutol alone. The combination was bacteriostatic. (B) Blood. Moxifloxacin activity was statistically better than the control (P < 0.05) but not superior to ethambutol.

FIG. 3

Effect of treatment of disseminated M. avium infection with moxifloxacin (MXF) (100 mg/kg) alone or in combination with ethambutol (EMB). (A) Liver. (B) Spleen. Moxifloxacin at 100 mg/kg, compared to the control at the same time point, was bacteriostatic (P < 0.05). The P value was <0.05 for the comparison between the combination moxifloxacin-ethambutol and the control at the same time point and for the comparison between the combination moxifloxacin-ethambutol and either moxifloxacin or ethambutol alone. The effect was bactericidal (P < 0.05 compared with the 1-week control).

FIG. 4

Effect of therapy for disseminated M. avium infection with moxifloxacin (MXF) alone and in combination with rifabutin (RBT) and/or azithromycin (AZI). (A) Liver. (B) Spleen. Thirty mice were used per group and per time point. P was <0.05 for all of the following comparisons: between moxifloxacin or azithromycin and the control; between the combination moxifloxacin-azithromycin and moxifloxacin and between the combination azithromycin-rifabutin and rifabutin alone; between the combinations moxifloxacin-azithromycin, moxifloxacin-rifabutin, azithromycin-rifabutin, and moxifloxacin-azithromycin-rifabutin and the untreated control at the same time point; between the combination azithromycin-moxifloxacin and moxifloxacin alone or azithromycin alone; between the combination azithromycin-rifabutin and rifabutin alone or azithromycin alone; and between the combination moxifloxacin-rifabutin and rifabutin alone or moxifloxacin alone. In the liver, the combination moxifloxacin-azithromycin was significantly (P < 0.05) less active than azithromycin alone. The combination of the three drugs was not more active than azithromycin alone (P > 0.05 for all comparisons), nor were the combinations azithromycin-moxifloxacin and azithromycin-rifabutin.