In vitro activity of cethromycin, a novel antibacterial ketolide, against Chlamydia pneumoniae.

OBJECTIVES To investigate the in vitro activity of cethromycin, a new ketolide, against Chlamydia pneumoniae. METHODS The in vitro activity of cethromycin against 20 isolates of C. pneumoniae was compared with the activities of telithromycin, erythromycin A, azithromycin and clarithromycin against those isolates. RESULTS The MIC at which 90% of the isolates were inhibited and the minimal chlamydiacidal concentration at which 90% of the isolates were killed by cethromycin were both 0.016 mg/L (range 0.016-0.031 mg/L). Cethromycin was the most active antibiotic tested in this study. CONCLUSIONS Our results appear to indicate that cethromycin is an effective antibiotic that should play some role in the treatment of respiratory tract infections caused by C. pneumoniae.