NEOMYCIN SULFATE

Chemistry - An aminoglycoside antibiotic obtained from Streptomyces fradiae, neomycin isactually a complex of three separate compounds, neomycin A (neamine; inactive), neomycin C andneomycin B (framycetin). The commercially available product almost entirely consists of the sulfatesalt of neomycin B. It occurs as an odorless or almost odorless, white to slightly yellow, hygroscopic powder or cryodessicated solid. It is freely soluble in water and very slightly soluble inalcohol. One mg of pure neomycin sulfate is equivalent to not less than 650 Units. Oral or injectable (after reconstitution with normal saline) solutions of neomycin sulfate have a pH from 5-7.5.

Storage, Stability, Compatibility

Neomycin sulfate oral solution should be stored at room temperature (15-30°C) in tight, light-resistant containers. Unless otherwise instructed by the manufacturer, oral tablets/boluses should be stored in tight containers at room temperature. The sterilepowder should be stored at room temperature and protected from light.
In the dry state, neomycin is stable for at least 2 years at room temperature.

Pharmacology - NEOMYCIN SULFATE

Neomycin has a mechanism of action and spectrum of activity (primarily gramnegative aerobes) similar to the other aminoglycosides, but in comparison to either gentamicin oramikacin, it is significantly less effective against several species of gram negative organisms, including strains of Klebsiella, E. coli and Pseudomonas. However, most strains of neomycin-resistant bacteria of these species remain susceptible to amikacin. More information on the aminoglycosides mechanism of action and spectrum of activity is outlined in more detail in the amikacin monograph.

Uses, Indications

Because neomycin is more nephrotoxic and less effective against severalbacterial species than either gentamicin or amikacin, its use is generally limited to the oral treatmentof enteral infections, to reduce microbe numbers in the colon prior to colon surgery, and orally or inenema form to reduce ammonia-producing bacteria in the treatment of hepatic encephalopathy.
Doses for parenteral administration are listed below, but should be used only with extreme cautiondue to the drug's toxic potential.

Pharmacokinetics - NEOMYCIN SULFATE

Approximately 3% of a dose of neomycin is absorbed after oral or rectal(retention enema) administration, but this can be increased if gut motility is slowed or if the bowelwall is damaged. Therapeutic levels are not attained in the systemic circulation after oraladministration.
After IM administration, therapeutic levels can be attained with peak levels occurring within 1 hourof dosing. The drug apparently distributes to tissues and is eliminated like the other aminoglycosides (refer to Amikacin monograph for more details). Orally administered neomycin is nearlyall excreted unchanged in the feces.

Contraindications, Precautions, Reproductive Safety

More detailed information on the contraindications, precautions and reproductive safety of the aminoglycoside antibiotics can be found inthe amikacin monograph.
Oral neomycin is contraindicated in the presence of intestinal obstruction or if the patient is hypersensitive to aminoglycosides.
Chronic usage of oral aminoglycosides may result in bacterial or fungal superinfections.
Because oral neomycin is only minimally absorbed, it is unlikely significant systemic or teratogenic effects should occur. However, one group of authors (Caprile and Short 1987) recommendsthat the drug not be used orally in foals.
Adverse Effects, Warnings,

Overdosage, Acute Toxicity

Refer to the amikacin monograph formore information regarding these topics with parenteral neomycin.
Rarely, oral neomycin may cause ototoxicity, nephrotoxicity, severe diarrhea and intestinalmalabsorption.
Drug Interactions, Drug/Laboratory Interactions - Refer to the amikacin monograph for moreinformation regarding drug interactions with parenteral neomycin. In addition: Oral neomycinshould not be given concurrently with oral penicillin VK as malabsorption of the penicillin mayoccur.
Oral neomycin with orally administered digitalis preparations (e.g., digoxin) may result in decreased absorption of the digitalis. Separating the doses of the two medications may not alleviatethis effect. Some human patients (<10%) metabolize digoxin in the GI tract and neomycin mayincrease serum digoxin levels in these patients. It is recommended that if oral neomycin is added orwithdrawn from the drug regimen of a patient stabilized on a digitalis glycoside, that enhancedmonitoring be performed.
Oral neomycin may decrease the amount of vitamin K absorbed from the gut; this may haveramifications for patients receiving oral anticoagulants.
Methotrexate absorption may be reduced by oral neomycin but is increased by oral kanamycin(found in Amforal®).
Although only minimal amounts of neomycin are absorbed after oral or rectal administration, theconcurrent use of other ototoxic or nephrotoxic drugs with neomycin should be done withcaution.