RiteMED Erythromycin Mechanism of Action

Pharmacologic Category: Antibacterial.
Pharmacology: Pharmacodynamics: Erythromycin inhibits protein synthesis by binding to the 50S ribosomal subunits of susceptible organisms, thereby inhibiting translocation of aminoacyl transfer-RNA and inhibiting polypeptide synthesis. As with other macrolide antibiotics, erythromycin readily penetrates into leukocytes and tissue macrophages.
Erythromycin is usually bacteriostatic, but may be bactericidal in high concentrations especially against highly susceptible organisms.
Pharmacokinetics: Erythromycin is readily absorbed after oral administration. Optimal serum levels of the drug are reached when taken in the fasting state or immediately before meals. Single oral doses of erythromycin generally produce peak serum concentrations within 1-4 hours. Higher peak serum concentrations are achieved when the drug is given four times a day than following single doses. Oral administration of erythromycin 250 mg, four times a day maintains antibacterial serum concentrations of 0.1 to 2 mcg/mL.
Erythromycin is widely distributed into most body tissues and fluids. Following oral administration of the drug, most tissues except the brain, have erythromycin concentrations that are higher and persist longer than serum concentrations. Only low concentrations of the drug (2-13% of serum concentrations) are distributed into the cerebrospinal fluid.
Erythromycin crosses the placenta, achieving fetal serum concentrations 5-20% of maternal serum concentrations. It is distributed into milk in concentrations about 50% plasma concentrations.
The serum half-life (t_1/2) of erythromycin in patients with normal renal function is usually 1.5-2 hours, but may range from 0.8-3 hours. In anuric patients, the serum t_1/2 may be prolonged to 6 hours, but this is not considered to be clinically important.
Erythromycin is partially metabolized by the cytochrome P-450 isoenzyme CYP3A4 in the liver by N-demethylation to inactive, unidentified metabolites. It is excreted mainly in the bile and undergoes intestinal absorption. About 2-5% of an oral dose is excreted in the urine. Only small amounts of erythromycin are removed by hemodialysis.
Microbiology: Antimicrobial Spectrum of Activity: Erythromycin is usually active against most strains of the following microorganisms both in vitro and in clinical infections: See Table 1.

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Erythromycin has demonstrated in vitro activity against the following microorganisms; however, clinical significance is unknown: Gram-positive organisms: Viridans group streptococci.
Gram-negative organisms: Moraxella catarrhalis.
It is suggested to carry out susceptibility tests.