Erythromycin

• Erythromycin is a macrolide antibiotic with a molecular formula of C37H67NO13 and a molecular mass of 733.93 g/mol. Its structure features a 14-membered lactone ring with two sugar moieties (desosamine and cladinose) attached, which are essential for its antibacterial activity. This structural configuration classifies it as the prototypical member of the macrolide family and serves as the foundation for later macrolides and azalides.
• The antibiotic exerts its bacteriostatic action by inhibiting bacterial protein synthesis. It specifically binds to the 50S ribosomal subunit, blocking the translocation of peptidyl-tRNA from the acceptor site to the donor site during translation. This mechanism prevents the elongation of peptide chains, effectively halting bacterial growth. At higher concentrations, erythromycin can also exhibit bactericidal activity against highly susceptible organisms.
• Erythromycin demonstrates broad-spectrum activity against a wide range of gram-positive bacteria, including Streptococcus pneumoniae, Streptococcus pyogenes, and Staphylococcus aureus. It is also effective against some gram-negative bacteria, such as Neisseria gonorrhoeae and Haemophilus influenzae, as well as atypical pathogens like Mycoplasma pneumoniae, Legionella pneumophila, and Chlamydia trachomatis. Additionally, it is used as an alternative for patients allergic to penicillin.
• The pharmacokinetic profile of erythromycin includes variable oral bioavailability (15-45%) due to degradation by gastric acid, necessitating the use of enteric-coated or esterified formulations (e.g., erythromycin estolate or ethylsuccinate) to improve absorption. It achieves widespread tissue distribution, with particularly high concentrations in the lungs, liver, and prostate. Erythromycin undergoes extensive hepatic metabolism, primarily by cytochrome P450 enzymes, and is excreted predominantly in bile, with a small fraction eliminated in urine. Its half-life ranges from 1.5 to 2 hours, typically requiring dosing every 6 to 8 hours.
• Despite its efficacy, erythromycin is associated with potential adverse effects, including gastrointestinal disturbances (e.g., nausea, vomiting, abdominal pain) due to its motilin receptor agonist activity, which can also lead to increased gastrointestinal motility. It is also known to prolong the QT interval, increasing the risk of cardiac arrhythmias, particularly in patients with pre-existing heart conditions or those taking other QT-prolonging medications.

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