Erythromycin uniquely has some potential benefit in the setting of gastroparesis. Azithromycin you will likely not see used for this indication.

Erythromycin binds the 50s subunit and ultimately prevents protein synthesis which is necessary for bacteria to grow and replicate.

QTc prolongation is a risk with all macrolide antibiotics (erythromycin included).

By inhibiting CYP3A4, erythromycin can be responsible for numerous drug interactions.