Telithromycin, the first ketolide antibiotic to undergo clinical development, has been specifically designed to treat community-acquired respiratory tract infections, including those caused by resistant pathogens. Like macrolides, telithromycin inhibits protein synthesis by acting mainly on the 50S ribosomal subunit. The defining structural characteristic is a keto function in place of the C3-cladinose moiety, which greatly improves acid stability and confers a lack of induction of MLSb resistance. Telithromycin provides potent activity against a wide spectrum of Gram-positive and Gram-negative organisms, including erythromycin-resistant pneumococci and atypical/intracellular organisms. Preliminary results from clinical trials have demonstrated that telithromycin may provide a convenient and effective compact treatment option for select respiratory tract infections such as community-acquired pneumonia, acute bacteria exacerbations of chronic bronchitis, acute sinusitis and tonsillitis/pharyngitis. (c) 2001 Prous Science. All rights reserved.