Erythromycin ethylsuccinate (E.E.S.®, ERY-PED®) is an ester of erythromycin base and succinic acid. It is suitable for oral administration. Erythromycin is a macrolide antibiotic, produced by Saccharopolyspora erythraea (formerly Streptomyces erythraeus). It acts primarily as a bacteriostatic agent. In sensitive organisms, it inhibits protein synthesis by binding to 50S ribosomal subunits. This binding process inhibits peptidyl transferase activity and interferes with translocation of amino acids during translation and assembly of proteins. Erythromycin does not affect nucleic acid synthesis.

Berythromycin or erythromycin B (also known as 12-deoxyerythromycin A), an acid-stable co-metabolite of the antibiotic erythromycin A, exhibits broad-spectrum antibiotic activity. The antibacterial activity of erythromycin B is similar to that of erythromycin A, but after acid-treatment, resembling exposure to the stomach, erythromycin B substantially retains antibacterial activity, whereas erythromycin A does not. Erythromycin B played an integral part of the structure activity relationship studies of semi-synthetic erythromycins.

Pseudoerythromycin A enol ether is devoid of antibiotic activity but can be used as an analytical standard for erythromycin A stability studies.

Erythromycin Oxime is the major metabolite of Roxithromycin which is also an intermediate of Azithromycin. It exhibits antibacterial properties and is also Roxithromycin impurity C.