List of products in the National Drug Code with proprietary name . Erythromycin is used to treat a wide variety of bacterial infections. It may also be used to prevent certain bacterial infections. Erythromycin is known as a macrolide antibiotic. It works by stopping the growth of bacteria. This antibiotic treats or prevents only bacterial infections. It will not work for viral infections (such as common cold, flu). Using any antibiotic when it is not needed can cause it to not work for future infections.