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.