erythromycin

Erythromycin is a macrolide antibiotic produced by Saccharopolyspora erythraea. It inhibits bacterial protein synthesis by binding reversibly to the 50S ribosomal subunit, blocking translocation and thereby preventing peptide chain elongation.

It is active primarily against Gram-positive bacteria, including many Streptococcus species and some Staphylococcus strains, and against atypical pathogens such as Mycoplasma pneumoniae, Chlamydophila spp., and Legionella pneumophila. It is used for respiratory tract infections, skin and soft tissue infections, and for patients who are penicillin allergic when the causative organisms are susceptible. Its use has declined in some settings due to rising resistance among common pathogens.

Erythromycin is available in oral and injectable forms, including erythromycin base and salt forms such as erythromycin estolate and erythromycin ethylsuccinate. Absorption is variable and can be reduced by certain formulations or food for some preparations; it is generally administered several times daily. It is primarily metabolized in the liver and excreted in bile; dosing and route depend on indication and formulation.

Common adverse effects include gastrointestinal upset (nausea, vomiting, diarrhea) and abdominal pain. Rare but serious effects include hepatotoxicity and QT interval prolongation, which can lead to torsades de pointes, especially with certain formulations or in combination with other QT-prolonging drugs. Erythromycin can inhibit cytochrome P450 enzymes, increasing levels of concomitant medications such as warfarin, theophylline, and certain statins. Bacterial resistance limits its effectiveness in some infections.

Erythromycin was discovered in Saccharopolyspora erythraea in the 1950s and has been used clinically since the mid-20th century. It remains a therapeutic option in select cases, particularly for patients who cannot tolerate beta-lactam antibiotics, though local resistance patterns guide its use.