COMPARATIVE ACTIVITIES OF AZITHROMYCIN AND CLARITHROMYCIN AGAINST MYCOBACTERIUM-AVIUM INFECTION IN BEIGE MICE

The comparative activities of azithromycin (AZI) and clarithromycin (C LA) against eight Mycobacterium avium complex (MAC) isolates were eval uated in the beige mouse model of disseminated infection. Mice were in fected 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 c ontrol animals. A dose-related reduction in organism cell counts in th e spleens between the groups receiving AZI at 100 and 200 mg/kg was ob served. 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 a ctive 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 a gainst organisms in the lungs was not significant for the remaining fi ve isolates. Clinical trials comparing the activities of AZI and CLA i n combination with other agents in patients with disseminated MAC infe ction are necessary to ascertain any clinically significant difference s in the efficacies of these agents.