Roxithromycin is a semi-synthetic macrolide antibiotic. It is very similar in composition, chemical structure and mechanism of action to erythromycin, azithromycin, or clarithromycin. Roxithromycin prevents bacteria from growing, by interfering with their protein synthesis. Roxithromycin binds to the subunit 50S of the bacterial ribosome, and thus inhibits the translocation of peptides. Roxithromycin has similar antimicrobial spectrum as erythromycin, but is more effective against certain gram-negative bacteria, particularly Legionella pneumophila. It can treat respiratory tract, urinary and soft tissue infections. It is not available in the United States, but is available in Australia.