Cethromycin is a ketolide antibiotic derived from erythromycin A being investigated for use in community-acquired pneumonia and other respiratory tract infections. Cethromycin possesses reliable activity against the bacteria most commonly associated with community-acquired pneumonia including S. pneumoniae, H. influenzae, M. catarrhalis, M. pneumoniae, C. pneumoniae, and L. pneumophila. Unlike fluoroquinolones, cethromycin has a narrower spectrum of activity against gram-negative bacteria, which may reduce the risk of collateral damage and the incidence of Clostridium difficile infection. It offers an advantage over telithromycin in that hepatotoxicity does not seem to be a concern. The FDA denied approval of cethromycin for the treatment of CAP in 2009, requesting more efficacy data.