Pharmacology: Pharmacodynamics: Erythromycin exerts antimicrobial action by binding to the 50S ribosomal sub-unit of susceptible microorganisms suppresses protein synthesis. Erythromycin is usually active against most strains of the following organisms both in vitro and in clinical infections: Gram positive bacteria - Listeria monocytogenes. Corynebacterium diphtheriae (as an adjunct to antitoxin), Staphylococci spp, Streptococci spp (including Enterococci).
Gram negative bacteria - Haemophilus influenzae, Neisseria meningitidis, Neisseria gonorrhoeae, Legionella pneumophila, Moraxella (Branhamella) catarrhalis, Bordetella pertussis, Campylobacter spp.
Mycoplasma - Mycoplasma pneumoniae, Ureaplasma urealyticum.
Other organisms - Treponema pallidum, Chlamydia spp, Clostridia spp, L-forms the agents using trachoma and lymphogranuloma venereum.
Note: The majority of strains of Haemophilus influenza are susceptible to the concentrations reached after ordinary doses.
Pharmacokinetics: Absorption: Erythromycin is adversely affected by gastric acid. For this reason, erythromycin tablets are enteric coated.
It is absorbed from the small intestine. It is widely distributed throughout body tissues.
Little metabolism occurs and only about 5% is eliminated in the urine. It is excreted principally by the liver.