Activity of ABT-773 against Mycobacterium avium complex in the beige mousemodel

ABT-773, a new ketolide antimicrobial agent, was evaluated in comparison to clarithromycin (CLA) in vitro against Mycobacterium avium complex (MAC) an d in a beige mouse model of disseminated MAC infection. The MICs at which 5 0 and 90% of the isolates tested were inhibited were 2 and 4 mu g/ml, respe ctively, for CLA and 8 and 16 mu g/ml, respectively, for ABT-773. Eight CLA -resistant isolates were found to be resistant to ABT-773 (MICs > 64 mu g/m l). In the in vivo study mice were treated with ABT-773 (50, 100, and 200 m g/kg of body weight) or CLA (200 mg/kg). Both ABT-773 (100 and 200 mg/kg) a nd CLA significantly decreased the viable cell counts in spleens and lungs. ABT-773 (200 mg/kg) and CLA had similar activities in lungs, but the forme r was more active in spleens.