Erythromycin A spiroketal;Anhydroerythromycin A;(1S,2R,3R,4S,5R,8R,9S,10S,11R,12R,14R)-11-[(2S,3R,4S,6R)-4-(dimethylamino)-3-hydroxy-6-methyloxan-2-yl]oxy-5-ethyl-3-hydroxy-9-[(2R,4R,5S,6S)-5-hydroxy-4-methoxy-4,6-dimethyloxan-2-yl]oxy-2,4,8,10,12,14-hexamethyl-6,15,16-trioxatricyclo[10.2.1.11,4]hexadecan-7-one
Methods of treating a microbial infection comprising administering to a patient in need of such treatment are disclosed. In one aspect the method comprises administering to a patient in need of such treatment a therapeutically effective amount of Erythromycin B (or a pharmaceutically acceptable derivative thereof). In another aspect the method comprises a pharmaceutical composition comprising at least 50% by weight of Erythromycin B (or a pharmaceutically acceptable derivative thereof) of the total weight of antibiotic present in the composition. Also disclosed are 2′-esters of Erythromycin B and Erythromycin B enol ether.