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.