Neomycin

Neomycin is a broad-spectrum aminoglycoside antibiotic derived from the metabolites of Streptomyces fradiae (a bacterium). Neomycin is a mixture of three components, neomycin A, B, and C. Neomycin B, also known as framycetin, is the most active component. Neomycin is active against both gram-positive and gram-negative pathogens and is used in the form of its sulfate salt against infections of the skin and mucous membranes and to treat open wounds or burns. In addition, it can be used in other preparations (orally or as a solution) to treat infections of the intestine and bladder, and to treat hepatic encephalopathy. It is often combined with other antibiotics. Neomycin is available only on prescription.

Pharmacodynamics

Like other aminoglycoside antibiotics, neomycin inhibits bacterial ribosomes by binding to the 30S ribosomal subunit of susceptible bacteria and interfering with the translation of bacterial protein synthesis. Bacterial translation is normally initiated by binding of mRNA to the 30S ribosomal subunit and subsequent binding to the 50S subunit for elongation. Binding of neomycin to the ribosomes prevents this from occurring and the bacteria from growing and reproducing.

Pharmacokinetics

Neomycin is poorly absorbed from the gastrointestinal tract. However, gastrointestinal absorption of the drug may be increased if inflammatory or ulcerative gastrointestinal disease is present. Protein binding ranges from 0-30%. There is limited information on the metabolism of neomycin, as systemic absorption after administration of the drug is vanishingly small. Therefore, metabolism is considered negligible. The small absorbed fraction of neomycin is excreted by the kidney. The unabsorbed portion of the drug is excreted unchanged in the feces.

Drug Interactions

Since neomycin does not enter the systemic circulation, serious interactions are not expected.

Side effects

When used topically, side effects are usually limited to the area of application and include skin irritation and redness and itching. In the systemic circulation, side effects may be severe. Possible side effects include severe hypotension, palpitations, shock, nausea and vomiting. Therefore, it is nowadays mostly used only in topical preparations.

Toxicological data

LD50 of neomycin sulfate (mouse,oral): > 8 g/kg.