Azalides such as azithromycin are a class of macrolide antibiotics that were originally manufactured in response to the poor acid stability exhibited by original macrolides (erythromycin). Following the clinical overuse of macrolides and azalides, ketolides have been developed to combat surfacing macrolide-azalide resistance among streptococci species.
Azalides, such as azithromycin, are a type of macrolide antibiotic designed to overcome the acid instability issues present in earlier macrolides (like erythromycin).  The widespread use of macrolides and azalides has resulted in the emergence of resistance among streptococci species, prompting the development of ketolides.