Erythromycin is a macrolide antibiotic which has a spectrum of activity which is similar to that of penicillin, often used in those who have an allergy to penicillins. For respiratory tract infections, it has better coverage of atypical organisms, including mycoplasma.

Otherwise a great antibiotic for treating community respiratory tract infections, a significant number of people unfortunately have serious gastrointestinal upset as a side-effect of this antibiotic so it tends not to be prescribed as a first-line drug.