In vitro activity of the ketolide ABT-773.

The in vitro activities of ABT-773, azithromycin, erythromycin, and clindamycin were compared by testing 1,223 clinical isolates selected to represent different species and phenotypes. ABT-773 was particularly potent against staphylococci (the MIC at which 90% of the strains tested were inhibited [MIC(90)] was < or =0.06 microg/ml), including all strains that were macrolide resistant but clindamycin susceptible. Streptococcus pneumoniae and other streptococci were inhibited by low concentrations of ABT-773, and that included most erythromycin-resistant strains. Against Haemophilus influenzae, ABT-773 and azithromycin were similar in their antibacterial potency (MIC(90), 4.0 and 2.0 microg/ml, respectively).