Erythromycin A is the first macrolide antibiotic identified in the fermentation media of the strain Saccharopolyspora erythraea( formerly known as Streptomyces erythreus). This posesses very good antibacterial activity against gram positive bacteria and mycoplasmas.
This is weak base hence absorbed from intestinal environment. But in acidic condition it is unstable and degraded by intramolecular cyclization and subsequent formation of spiroketal derivative anhydroerythromycin A. To overcome this problem various water insoluble acid stable salt or esters were prepared. acetate, propionate, ethyl succinate esters were found to acid stable. these esters were prepared by acetylation of 2' -OH group of erythromycin A. These esters are also capable of masking bitter taste of the drug and are useful in pediatric preparation. Though there are various semisynthetic macrolides such as Roxithromycin, Clarithromycin, Azithromycin etc. are acid stable shows good oral bioavailability.
