Activities of azithromycin and clarithromycin against nontuberculous mycobacteria in beige mice

The comparative activities of azithromycin (AZI) and clarithromycin (CLA) were evaluated against nontuberculous mycobacteria in a murine model of disseminated infection. Four-week-old beige mice (C57BL/6J bgj/bgj) were infected intravenously with approximately 10(7) viable Mycobacterium kansasii, M. xenopi, M. simiae, or M. malmoense. Treatment with AZI at 200 mg/kg, CLA at 200 mg/kg, ethambutol at 125 mg/kg, rifampin at 20 mg/kg, or clofazimine at 20 mg/kg of body weight was started 7 days postinfection, and the treatments were administered 5 days per week for 4 weeks. Control groups were sacrificed at the start and end of the treatments. Spleens and lungs were homogenized, and viable cell counts were determined by serial dilution and plating onto 7H10 agar. AZI and CLA had activities comparable to or better than that of rifampin, ethamutol, or clofazimine against these nontuberculous mycobacteria in the beige mouse test system. AZI at 200 mg/kg was more active than CLA at 200 mg/kg against organisms in the spleens for M. xenopi and M. malmoense. The activities of AZI and CLA were comparable against organisms in the spleens for M. kansasii and M. simiae. The activities of these two agents were comparable against organisms in the lungs for all four nontuberculous mycobacterial species. AZI or CLA in combination with other agents may be useful for the therapy of nontuberculous mycobacterial infections in humans.