Telithromycin (HMR3647) is a ketolide antibiotic to treat community acquired pneumonia of mild to moderate severity. Antibacterial Telithromycin prevents bacteria from growing, by interfering with their protein synthesis. Telithromycin binds to the subunit 50S of the bacterial ribosome, and blocks the progression of the growing polypeptide chain. Telithromycin has over 10 times higher affinity to the subunit 50S than erythromycin. In addition, telithromycin strongly bind simultaneously to two domains of 23S RNA of the 50 S ribosomal subunit, where older macrolides bind strongly only to one domain and weakly to the second domain. Telithromycin can also inhibit the formation of ribosomal subunits 50S and 30S.