Telithromycin antibiotic molecule. Computer model of a molecule of the antibiotic telithromycin, which is marketed as Ketek. Atoms are represented as spheres and are colour-coded: carbon (green), hydrogen (white), oxygen (red) and nitrogen (blue). Telithromycin is a semi-synthetic drug derived from erythromycin. It kills bacteria by binding to their ribosomes, the site of protein synthesis, and blocking them. It is used to treat mild to moderate respiratory infections.