| Indication |
Topical uses include treatment for superficial eye infections caused by susceptible bacteria (used in combination with other antiinfectives), treatment of otitis externa caused by susceptible bacteria, treatment or prevention of bacterial infections in skin lesions, and use as a continuous short-term irrigant or rinse to prevent bacteriuria and gram negative rod bacteremia in abacteriuric patients with indwelling catheters. May be used orally to treat hepatic encephalopathy, as a perioperative prophylactic agent, and as an adjunct to fluid and electrolyte replacement in the treatment of diarrhea caused to enteropathogenic E. coli (EPEC). |
| Mechanism of action |
Aminoglycosides like neomycin "irreversibly" bind to specific 30S-subunit proteins and 16S rRNA. Specifically neomycin binds to four nucleotides of 16S rRNA and a single amino acid of protein S12. This interferes with decoding site in the vicinity of nucleotide 1400 in 16S rRNA of 30S subunit. This region interacts with the wobble base in the anticodon of tRNA. This leads to interference with the initiation complex, misreading of mRNA so incorrect amino acids are inserted into the polypeptide leading to nonfunctional or toxic peptides and the breakup of polysomes into nonfunctional monosomes. |
| Absorption |
Poorly absorbed from the normal gastrointestinal tract. Although only approximately 3% of neomycin is absorbed through intact intestinal mucosa, significant amounts may be absorbed through ulcerated or denuded mucosa or if inflammation is present. |
| Protein binding |
Protein binding studies have shown that the degree of aminoglycoside protein binding is low and, depending upon the methods used for testing, may be between 0% and 30%. |
| Biotransformation |
Neomycin undergoes negligible biotransformation after parenteral administration. |
| Route of elimination |
The small absorbed fraction is rapidly distributed in the tissues and is excreted by the kidney in keeping with the degree of kidney function. |
| Toxicity |
LD50 = 200 mg/kg (rat). Because of low absorption, it is unlikely that acute overdosage would occur with oral neomycin. However, prolonged administration could result in sufficient systemic drug levels to produce neurotoxicity, ototoxicity and/or nephrotoxicity. Nephrotoxicity occurs via drug accumulation in renal proximal tubular cells resulting in cellular damage. Tubular cells may regenerate despite continued exposure and nephrotoxicity is usually mild reversible. Neomycin is the most toxic aminoglycoside agent, which is thought to be due to its large number of cationic amino groups. Otoxocity occurs via drug accumulation in the endolymph and perilymph of the inner ear causing irreversible damage to hair cells in the cochlea or summit of ampullar cristae in the vestibular complex. High frequency hearing loss is followed by low frequency hearing loss. Further toxicity may cause retrograde degeneration of the auditory nerve. Vestibular toxicity may result in vertigo, nausea and vomiting, dizziness and loss of balance. |
| Affected organisms |
- Enteric bacteria and other eubacteria
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