Erythromycin antibiotic pills. Capsules of Erymax (250mg) containing the antibiotic drug erythro- mycin. This is a broad-spectrum anti-bacterial drug, from the aminoglycoside group of antibiotic drugs. Erythromycin is used to treat bacterial infections of the skin, chest, throat, and ears. It is especially useful in treating whooping cough (pertussis) and Legionnaire's disease. In young children, under 8 years of age, erythromycin is an alternative antibiotic to using the drug tetracycline which can permanently stain developing teeth.