Neomycin

Absorption

Neomycin is poorly absorbed from the gastrointestinal tract. Gastrointestinal absorption of the drug may be increased if inflammatory or ulcerative gastrointestinal disease is present.

Toxicity

The oral LD50 of neomycin sulfate in mouse is > 8 g/kg. The subcutaneous LD50 is 200 mg/kg in rat and 190 mg/kg in mouse. The intraperitoneal LD50 in mouse is 305 mg/kg. The oral Lowest published toxic dose (TDLo) in woman is 12600 mg/kg/7D.
Because of low absorption, acute overdosage from oral neomycin is not likely to occur. However, prolonged administration of neomycin should be avoided because of the possibility of some systemic absorption and the risk of neurotoxicity, ototoxicity, and/or nephrotoxicity. Hemodialysis will remove neomycin from the blood. While nephrotoxicity and ototoxicity have been reported in otherwise patients without compromised renal function, the risk for developing these toxicities is increased in patients with renal impairment. Like other aminoglycosides, neomycin may cause fetal harm and total irreversible bilateral congenital deafness when administered in pregnant women.

Description

Neomycin is an antibiotic from the aminoglycoside group, and has two isomers - neomycin Band neomycin C. Occupational contact dermatitis mainly occurs in workers at animal-feed mills, in veterinaries and in health workers.

Originator

Myciguent,Upjohn,US,1951

The Uses of Neomycin

Neomycin, like streptomycin, has a broad spectrum of antibacterial activity. It is effective with respect to the majority of Gram-negative and a few Gram-positive bacteria; staphylococci, pneumococci, gonococci, meningococci, and stimulants of dysentery. It is not very active with respect to streptococci. The antibiotic effect of neomycin with respect to many types of bacteria is higher than that of streptomycin. At the same time, microorganisms sensitive to neomycin become resistant to a lesser degree than streptomycin.
It is used for various gastrointestinal diseases caused by microorganisms sensitive to it, including enteritis, which is caused by microbes that are resistant to antibiotics. However, because of its high oto- and nephrotoxicity, its local use is preferred for infected skin diseases, infected wounds, conjunctivitis, keratitis, and others. Synonyms of this drug are framycetin, soframycin, tautomycin, and others.

The Uses of Neomycin

Antibacterial; antifungal.

The Uses of Neomycin

Neomycin is an antibiotic.

Indications

Oral neomycin sulfate is indicated as an adjunctive therapy in hepatic coma (portal-system encephalopathy) by reducing ammonia-forming bacteria in the intestinal tract. It is strongly recommended that oral neomycin is only used in infections that are proven or strongly suspected to be caused by susceptible bacteria to reduce the risk of the development of drug-resistant bacteria.
Neomycin, in combination with polymyxin B sulfates and hydrocortisone in otic suspensions, is used in the treatment of superficial bacterial infections of the external auditory canal caused by organisms susceptible to the antibiotics. This otic formulation is also used in the treatment of infections of mastoidectomy and fenestration cavities caused by organisms susceptible to the antibiotics.
The ophthalmic solution containing neomycin in combination with polymyxin B sulfates and dexamethasone is used to treat steroid-responsive inflammatory ocular conditions for which a corticosteroid is indicated and where bacterial infection or a risk of bacterial infection exists.

Background

Neomycin is a broad-spectrum aminoglycoside antibiotic drug that is derived from the metabolic products of Streptomyces fradiae. Neomycin is a complex comprised of three components, neomycin A, B, and C. Neomycin B, also known as framycetin, is the most active component of the complex and neomycin C is the isomer of neomycin B, making these two stereoisomers the active components of neomycin. Neomycin A, or neamine, is a moiety that conjoins two molecules of neomycin B and C together. Neomycin is active against both gram-positive and gram-negative organisms and mediates its pharmacological action by binding to bacterial ribosomes and inhibiting protein synthesis, which is crucial for the survival of bacteria.
Neomycin sulfate is the most common form for pharmaceutical preparations; because the compound is a complex, the amount of neomycin in products is measured in units. Neomycin sulfate as monotherapy is available in an oral solution for adjunct use in the treatment of hepatic coma. It is also used in combination with polymyxin B sulfates and hydrocortisone in otic suspensions for use in the treatment of bacterial infections in the external auditory canal, including infections caused by medical procedures in the ear. Neomycin is also used in combination with polymyxin B sulfates and dexamethasone in ophthalmic preparations for use in the treatment of inflammatory conditions and infections in the eye. Neomycin is also available in over-the-counter topical products to prevent minor skin infections.

Definition

An antibiotic complex obtained from Streptomyces fradiae; it is soluble in water and methanol but insoluble in most organic solvents. It consists of three component substances, all of which function as antiinfective agents; some derivatives have fungicidal properties. The three types are A (also called neamine): C12H26N4O6; B: C 23H46N6O13 (also available as hydrochloride and sulfate); and C: C23H46O13

Manufacturing Process

Neomycin has been produced by growing the organism, Strepromyces No. 3535, in a suitable nutrient medium under appropriate stationary or submerged aerobic (viz shaken) conditions, and then isolating and purifying the substance, e.g., by procedure of the sort described in the figure including various steps of adsorption, recovery by elution, separation from impurities, and precipitation.
Neomycin is usually used as the sulfate.

brand name

Mycifradin (Pharmacia & Upjohn); Neo-Fradin (X Gen); Neobiotic (Pfizer).

Therapeutic Function

Antibacterial

Antimicrobial activity

Among other organisms susceptible in vitro (MIC 4–8 mg/L) are Pasteurella, Vibrio, Borrelia and Leptospira spp. It is active against M. tuberculosis, including streptomycin-resistant strains. Synergy has been reported with polymyxin B. The bactericidal effect is enhanced at alkaline pH.

Acquired resistance

Resistance is acquired in a stepwise fashion and staphylococci may become resistant as a result of prolonged topical use. The use of neomycin–bacitracin–polymyxin mixtures may contribute to this, as many strains resistant to neomycin are also resistant to bacitracin. Resistant enterobacteria may appear in the feces of patients treated orally and in those treated for prolonged periods; most have been found to possess multiple transferable antibiotic resistance. Cross-resistance with kanamycin is often due to the synthesis of APH(3′), although AAC(6′) some forms of AAC(3) and ANT(4′) also modify both neomycin and kanamycin. Resistant strains of Staph. aureus are usually more resistant to kanamycin than to neomycin. The rare enzyme AAC(1) confers resistance to neomycin and paromomycin, but not to other aminoglycosides.

Contact allergens

Neomycin is an antibiotic complex of the aminoglycosides group, extracted from Streptomyces fradiae. It is composed of neomycin A (neamin) and an isomer neobiosamin, either neomycin B (framycetin or Soframycin?) or neomycin C. Its use has been progressively forbidden in cosmetics and as an additive for animal feed. Occupational contact dermatitis occurs in workers at animal feed mills, in veterinaries, or in health workers. Nonoccupational dermatitis mainly concerns patients with chronic dermatitis, leg ulcers, or chronic otitis. Cross-sensitivity is usual with other aminoglycosides (amikacin, arbekacin, butirosin, dibekacin, gentamicin, isepamicin, kanamycin, paromomycin, ribostamycin, sisomycin, tobramycin), is rare with netilmicin and streptomycin, but nonexistent with spectinomycin.

Mechanism of action

Neomycin has a wide spectrum of antibacterial action. It is effective against both a number of Gram-positive as well as Gram-negative microorganisms. However, it is able to bind with cholesterol and bile salts. In combination with other bile salt-reducing drugs or nicotinic acid, neomycin is able to block cholesterol and bile salt absorption, which significantly increases the level of cholesterol in the plasma.

Pharmacokinetics

Neomycin mediates its bactericidal action by inhibiting bacterial protein synthesis, thereby suppressing the growth and survival of susceptible bacteria. Following oral administration, the duration of bactericidal activity of neomycin ranged from 48 to 72 hours. By decreasing colonic bacteria that produce ammonia, neomycin was shown to be effective as an adjunctive therapy in hepatic coma to improve neurologic symptoms.
Neomycin is active against both gram positive and gram negative organisms, including the major E. coli species resident in the colon as well as the enteropathogenic forms of E. coli. It is also active against Klebsiella-Enterobacter group. Resistant strains of E. coli, Klebsiella and Proteus spp. may emerge from neomycin therapy. Neomycin has no antifungal activity and has some activity against some protozoa.

Pharmacokinetics

C_{max 0.5 g intramuscular: 20 mg/L after 1 h
Plasma half-life: 2–3 h
Volume of distribution: 0.25–0.35 L/kg
Plasma protein binding: Low
Very little is absorbed after oral administration and more than 95% is eliminated unchanged in the feces. Peak plasma concentrations of less than 4 mg/L have been found after an oral dose of 3 g. Distribution and excretion resemble that of streptomycin, but the toxicity of neomycin precludes systemic administration except in the most extreme cases.}

Clinical Use

Superficial infections with staphylococci and Gram-negative bacilli (topical; alone or in combination with bacitracin, chlorhexidine or polymyxin)
Treatment of staphylococcal nasal carriers (topical, in combination with chlorhexidine or bacitracin)
Eye infections (topical; alone or in combination)
Otitis externa (alone or with a corticosteroid)
Gut decontamination before abdominal surgery (oral)
Prophylaxis after urinary tract instrumentation (instillation)
Use is discouraged because of the possibility of promoting the appearance of aminoglycoside-resistant strains, and because of the risk of absorption with the consequent danger of systemic toxicity or neuromuscular blockade.

Side Effects

Neomycin is the most likely of all the aminoglycosides to damage the kidneys and the auditory branch of the eighth nerve. This has almost entirely restricted it to topical and oral use.
Irreversible deafness may develop even if the drug is stopped at the first sign of damage. Loss of hearing may occur as a result of topical applications to wounds or other denuded areas, particularly if renal excretion is impaired. Instillation of ear drops containing neomycin can result in deafness. This generally develops in the second week of treatment and is usually reversible.
Rashes have been described in 6–8% of patients treated topically and these patients may be rendered allergic to other aminoglycosides. Nausea and protracted diarrhea may follow oral administration. Sufficient drug may be absorbed from the gut on prolonged oral administration to produce deafness but not renal damage. Intestinal malabsorption and superinfection have been seen in patients receiving 4–9 g per day and may develop in patients receiving as little as 3 g of the drug per day. Precipitation of bile salts by the drug may impair the hydrolysis of long-chain triglycerides. Large doses instilled into the peritoneal cavity at operation may be absorbed, with resultant systemic toxicity, and patients concurrently exposed to anesthetics and muscle relaxants are liable to suffer neuromuscular blockade, which is reversible by neostigmine.

Safety Profile

Poison by intraperitoneal, intravenous, and subcutaneous routes. Moderately toxic by ingestion. Human systemic effects: changes in hearing acuity, liver tubule changes, and decreased urine volume or anuria. Mutation data reported. When heated to decomposition it emits acrid smoke and irritating fumes.

Synthesis

Neomycin is a complex mixture of antibiotics (neomycins A, B, C, D, E, and F), that is formed by the actinomycete S. fradiae. Neomycin A, also called neamine, is 2-deoxy-4-O-(2,6-diamino-2,6-dideoxy-α-D-glucopyranosyl)-D-streptamine (32.4.2), and it does not display antibiotic properties. At the same time, neomycin B, O-2,6-diamino- 2,6-dideoxy-α-D-glucopyranosyl(1→4)-O-[O-2,6-diamino-2,6-dideeoxy-β-L-idopyranosyl-(1→3)-β-D-ribofuranosyl-(1→5)]-2-deoxy-D-streptamine (32.4.3), differs from neomycin A in the presence a second glycoside residue and exhibits powerful antibacterial activity. Neomycin C (32.4.4) differs from neomycin B in the orientation of the aminomethyl group in the neozamine part of the molecule.

Metabolism

There is limited information on the metabolism of neomycin, as there is limited systemic absorption following drug administration. Metabolism is deemed to be negligible.