HMR 3004 (also known as RU 64004) is a chemical compound classified as a ketolide. Ketolides are a novel class of semisynthetic 14-membered-ring macrolide antibiotics derived from erythromycin A. The distinguishing feature of ketolides like HMR 3004 is the presence of a 3-keto group on the erythronolide A ring instead of the l-cladinose sugar found in traditional macrolides like erythromycin.