Intermittent azithromycin for treatment of Mycobacterium avium infection in beige mice.

The activity of azithromycin (AZI) was evaluated in the beige mouse model of disseminated Mycobacterium avium infection. Mice were infected intravenously with approximately 10(7) viable avium ATCC 49601. AZI at 50, 100, or 200 mg/kg of body weight or clarithromycin (CLA) at 200 mg/kg was given by gavage 5 days per week for 4 weeks. Groups of treated mice were compared with untreated control animals. A dose-related reduction in cell counts in organs was observed with AZI treatment. AZI at 200 mg/kg was more active than CLA at 200 mg/kg against organisms in spleens. The activities of these two agents at 200 mg/kg were comparable against organisms in lungs. In a second study, AZI at 200 mg/kg was given daily for 5 days; this was followed by intermittent AZI treatment for the next 3 weeks. The activities of AZI given on a three-times- and five-times-per-week basis in the continuation phase were comparable. AZI given on a once-weekly basis was less active. The regimen of AZI given in combination with rifapentine on a once-weekly basis for 8 weeks showed promising activity. Clinical evaluation of AZI and rifapentine will help to define the roles of these agents in the treatment of disseminated M. avium complex infection.