Erythromycin has an adequate penetration to most body tissues except cerebrospinal and synovial fluids. Depending on drug concentration, bacterial species, density of inoculum and phase of growth, erythromycin may act as bacteriostatic or bactericidal. It acts by inhibiting RNA dependent protein synthesis at the site of chain elongation by binding to the 50 S ribosomal subunit, resulting in blockage of transpeptidation and translocation reactions. Erythromycin is the drug of choice for M. pneumonia infections, Legionella pneumonia, chlamydia infections, ureoplasma infections, pertussis, diphtheria, and prophylaxis against H. influenza and N. meningitis infections. It also plays an important role as an alternative drug to penicillin and as part of empiric treatment of the seriously ill adult with community-acquired pneumonia.
Intramuscular administration is avoided because of severe pain on injection.
Erythromycin is also available as an ophthalmic ointment and in topical preparations. QT prolongation can last as long as 4 days after stopping the drug. QT prolongation was observed in 12 of 13 erythromycin infusions in 7 critically ill patients, with a direct correlation between extent of QT prolongation and infusion rate. Most of the cases reported occurred in patients receiving IV erythromycin lactobionate, suggesting a role for the lactobionate product with respect to the observed cardiotoxicity. It appears to be a hypersensitivity reaction to the estolate compound.