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
Uses
Antibacterial; antifungal.
Uses
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.
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.
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
Cmax 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.
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.
