Comparative activities of azithromycin and clarithromycin against Mycobacterium avium infection in beige mice

The comparative activities of azithromycin (AZI) and clarithromycin (CLA) against eight Mycobacterium avium complex (MAC) isolates were evaluated in the beige mouse model of disseminated infection. Mice were infected intravenously with approximately 10(7) viable MAC isolate. AZI at 100 or 200 mg/kg of body weight or CLA at 200 mg/kg of body weight was given by gavage daily for 10 days starting at 7 days postinfection. In each study, groups of treated mice were compared with untreated control animals. A dose-related reduction in organism cell counts in the spleens between the groups receiving AZI at 100 and 200 mg/kg was observed. AZI at 200 mg/kg was more active than CLA at 200 mg/kg against six of eight MAC isolates in the spleens. CLA at 200 mg/kg was more active than AZI at 200 mg/kg against three of eight MAC isolates in the lungs. The difference between AZI at 200 mg/kg and CLA at 200 mg/kg against organisms in the lungs was not significant for the remaining five isolates. Clinical trials comparing the activities of AZI and CLA in combination with other agents in patients with disseminated MAC infection are necessary to ascertain any clinically significant differences in the efficacies of these agents.