Neomycin Sulfate

Aminoglycoside Antibiotic Antibacterial

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO 10-20 mg/kg q6-12h Duration: 3-5 days
Notes: For diarrhea; use with caution in renal impairment.
Cat PO 10-20 mg/kg q6-12h Duration: 3-5 days
Notes: Use with caution; may cause GI upset.
Horse (foal) PO 10-20 mg/kg q6-12h Duration: 3-5 days
Notes: For diarrhea; monitor hydration.
Cattle (calf) PO 10-20 mg/kg q12h Duration: 3-5 days
Notes: For diarrhea; observe withdrawal times.
Cattle (lactating) Intramammary One tube per affected quarter q12h Duration: 3-5 days
Notes: Use only in lactating cows; follow label instructions.
Dog, Cat Topical (otic/ophthalmic) Apply 2-4 drops per affected ear/eye q6-12h Duration: 7-14 days
Notes: Use combination products as directed.

Clinical Indications & Species Uses

General Indications
  • Oral: for enteric infections caused by susceptible Gram-negative bacteria
  • Topical: for skin, eye, and ear infections (often in combination with other antibiotics and corticosteroids)
  • Intramammary: for treatment of mastitis in lactating cows
Dog (Canine)
  • Treatment of bacterial diarrhea caused by susceptible organisms (e.g., E. coli)
  • Reduction of ammonia-producing bacteria in hepatic encephalopathy (adjunctive therapy)
  • Topical treatment of skin infections (in combination with other antibiotics)
Cat (Feline)
  • Treatment of bacterial diarrhea (less common)
  • Topical treatment of skin infections (in combination products)
Horse (Equine)
  • Treatment of bacterial diarrhea (foals)
  • Topical treatment of wounds and infections
Cattle (Bovine)
  • Treatment of bacterial diarrhea (calves)
  • Topical treatment of mastitis (intramammary preparations)
Small Ruminants (Sheep / Goat)
  • Treatment of bacterial diarrhea (lambs, kids)
  • Topical treatment of infections
Rabbit & Small Mammals
  • Treatment of bacterial enteritis (use with caution due to risk of dysbiosis)
Avian & Poultry
  • Treatment of bacterial enteritis (in water medication)

Pharmacology & Mechanism of Action

Drug Class: Aminoglycoside Antibiotic | Pharmacological Group: Antibacterial

Mechanism of Action: Neomycin is an aminoglycoside antibiotic that binds irreversibly to the 30S ribosomal subunit of susceptible bacteria, causing misreading of the genetic code and inhibition of protein synthesis. It is bactericidal and primarily effective against aerobic Gram-negative bacilli and some Gram-positive organisms. Its action is concentration-dependent and exhibits a post-antibiotic effect.

Pharmacodynamics: Neomycin is active against many aerobic Gram-negative bacteria including E. coli, Klebsiella, Proteus, Enterobacter, and Salmonella. It has limited activity against Gram-positive cocci and is ineffective against anaerobes, Pseudomonas aeruginosa, and most streptococci. Resistance can occur via plasmid-mediated enzymes that modify the drug, reducing its affinity for the ribosome.

⚑ Pharmacokinetics Summary

Absorption: Neomycin is poorly absorbed from the gastrointestinal tract; less than 3% of an oral dose is absorbed. Absorption may be increased in patients with inflammatory bowel disease or hepatic dysfunction. After parenteral administration, it is rapidly absorbed.
Distribution: Following absorption, neomycin distributes into extracellular fluids. It does not penetrate the blood-brain barrier well, but crosses the placenta. It accumulates in the renal cortex and inner ear, which is the basis for its nephrotoxicity and ototoxicity.
Metabolism: Neomycin is not significantly metabolized; it is excreted unchanged.
Excretion: The absorbed fraction is excreted primarily by glomerular filtration in the urine. The unabsorbed oral dose is eliminated in feces. In animals with normal renal function, the elimination half-life is approximately 2-3 hours, but it is prolonged in renal impairment.
Half-Life: 2-3 hours (systemic, in animals with normal renal function)
Bioavailability: Oral: <3% (systemic); Topical: minimal systemic absorption.
Protein Binding: Low; less than 10% bound to plasma proteins.

Available Formulations & Strengths

Oral Tablet 50 mg, 100 mg, 200 mg (PO)
Oral Solution 50 mg/mL, 100 mg/mL (PO)
Topical Ointment/Cream 0.5% (often in combination with other antibiotics) (Topical)
Ophthalmic Solution/Ointment 0.35% (often in combination) (Ophthalmic)
Otic Solution/Suspension 0.5% (often in combination) (Otic)
Intramammary Infusion 500 mg per syringe (Intramammary)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to neomycin or other aminoglycosides
  • Pre-existing renal disease or hearing impairment
  • Intestinal obstruction or severe ulcerative bowel lesions (oral use)
  • Concurrent use with other nephrotoxic or ototoxic drugs (e.g., other aminoglycosides, loop diuretics, cisplatin)
Warnings & Clinical Precautions:
  • Use with caution in animals with renal insufficiency; adjust dose or avoid systemic use.
  • Prolonged use may result in overgrowth of non-susceptible organisms, including fungi.
  • Oral neomycin may alter intestinal flora, leading to diarrhea or malabsorption.
  • In food animals, observe withdrawal times to avoid violative residues.
  • Avoid use in horses with diarrhea due to risk of endotoxemia? (Actually, neomycin may be used, but caution with dehydration).
  • Topical use on large wounds may result in systemic absorption.
  • Do not use in animals with known hypersensitivity to aminoglycosides.

Adverse Effects & Reactions

Common:

  • Gastrointestinal upset (nausea, vomiting, diarrhea) after oral administration
  • Local irritation at application site (topical)
  • Superinfection with resistant bacteria or fungi

Serious / Severe:

  • Nephrotoxicity (especially with systemic absorption or prolonged use)
  • Ototoxicity (cochlear and vestibular damage)
  • Neuromuscular blockade (respiratory paralysis) with high doses or concurrent anesthesia

Rare:

  • Allergic reactions (urticaria, anaphylaxis)
  • Hepatotoxicity (rare)
  • Malabsorption syndrome with prolonged oral use

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Other aminoglycosides (e.g., gentamicin, amikacin) Additive nephrotoxicity and ototoxicity High
Loop diuretics (e.g., furosemide) Increased risk of ototoxicity High
Neuromuscular blocking agents (e.g., atracurium, succinylcholine) Enhanced neuromuscular blockade, respiratory depression High
Polymyxin B Additive nephrotoxicity and neuromuscular blockade High
Cephalosporins (parenteral) Additive nephrotoxicity Moderate
Methoxyflurane (anesthetic) Increased risk of nephrotoxicity Moderate

Overdose & Toxicity Management

Signs of Toxicity:

  • Nephrotoxicity (increased BUN/creatinine, proteinuria)
  • Ototoxicity (hearing loss, ataxia, head tilt)
  • Neuromuscular blockade (muscle weakness, respiratory depression)
  • Gastrointestinal signs (vomiting, diarrhea) with oral overdose

Emergency Treatment Protocol: There is no specific antidote. Treatment is symptomatic and supportive. For oral overdose, consider gastric lavage or activated charcoal to reduce absorption. For systemic toxicity, discontinue drug, provide fluid therapy to maintain renal perfusion, and monitor renal function. In severe cases, hemodialysis or peritoneal dialysis may be considered. Neuromuscular blockade may be reversed with calcium salts or neostigmine (with atropine), but this is not always effective.

Food Animal Withdrawal Times

πŸ₯© Meat: 30 daysπŸ₯› Milk: 7 days

Withdrawal times vary by formulation and country. For oral use in cattle, meat withdrawal is typically 30 days; for intramammary use, milk withdrawal is 7 days. Always follow label and local regulations.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature (20-25Β°C or 68-77Β°F). Protect from freezing.

Handling & Special Conditions: Keep container tightly closed. Protect from moisture. For oral solutions, use within 30 days after opening.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved for oral use in dogs, cats, cattle, and swine; topical and intramammary preparations are approved for various species. Some products are available over-the-counter, but veterinary prescription may be required depending on formulation.

Extra-Label (Off-Label) Use: In the US, extra-label use of neomycin in food animals is prohibited if it results in violative residues. Under AMDUCA, extra-label use is permitted only by or on the order of a veterinarian within a valid VCPR, and only when no approved drug is available. Extra-label use in feed is prohibited.

Clinical Pearls & Practice Notes

πŸ’‘ Clinical Insights: Neomycin is primarily used orally for enteric infections and topically for skin, ear, and eye infections. Systemic use is limited due to nephrotoxicity and ototoxicity. It is often combined with other antibiotics (e.g., bacitracin, polymyxin B) and corticosteroids in topical preparations. In food animals, strict adherence to withdrawal times is essential. Use with caution in animals with renal impairment or dehydration. Monitor renal function if used systemically or in high doses. For diarrhea, ensure adequate hydration and consider supportive care. Neomycin is not effective against anaerobes, so it should not be used as a sole agent for mixed infections.

References & Literature

  • πŸ“š Plumb's Veterinary Drug Handbook
  • πŸ“š Papich Veterinary Pharmacology and Therapeutics
  • πŸ“š Compendium of Veterinary Products (CVP)