Neomycin
**Neomycin** is a broad-spectrum, bactericidal **aminoglycoside antibiotic** primarily effective against gram-negative aerobes. Because it is significantly more nephrotoxic than other aminoglycosides (like gentamicin or amikacin) when given systemically, its use in veterinary medicine is largely restricted to: * **Topical applications** (skin, eyes, ears) * **Oral administration** for enteric infections or "gut sterilization" prior to surgery * **Hepatic encephalopathy** management (to reduce ammonia-producing bacteria in the colon) > **Clinical Pearl:** Like all aminoglycosides, neomycin exhibits **concentration-dependent bactericidal activity** and a significant post-antibiotic effect (PAE). However, it is poorly absorbed from an intact gastrointestinal tract (only ~3%), making it ideal for local action within the gut lumen while minimizing systemic toxicity.
Mechanism: Neomycin actively transports across the bacterial cell membrane (an **oxygen-dependent** process, hence its lack of efficacy against anaerobes). It irreversibly binds to the **30S ribosomal subunit** โ causes misreading of mRNA โ inhibits protein synthesis โ leads to rapid bacterial cell death.
Dosing by species
- Hepatic encephalopathy ยท 22 mg/kg q8h PO ยท PO ยท q8h
- Hepatic encephalopathy ยท 20 mg/kg PO q8-12h ยท PO ยท q8-12h ยท Used with or without lactulose.
- Hepatic encephalopathy (stable animals) ยท 20 mg/kg PO q12h ยท PO ยท q12h ยท Avoid if evidence of intestinal bleeding, ulcerations, or renal failure.
- Campylobacteriosis ยท 20 mg/kg PO q12h ยท PO ยท q12h
- Systemic therapy ยท 3.5 mg/kg IV , IM or SC q8h ยท IV/IM/SC ยท q8h ยท Caution: Very nephrotoxic.
- Susceptible enteral infections (Young pigs) ยท 0.75-1 grams/day, PO divided 2-4 times daily at regular intervals ยท PO ยท divided 2-4 times daily ยท Doses are not standardized; use for general guidance only.
- Susceptible enteral infections ยท 7-12 mg/kg, PO q12h ยท PO ยท q12h
- Susceptible enteric infections ยท 10-20 mg/kg, PO twice to four times daily ยท PO ยท q6-12h
- Susceptible enteral infections (Lambs) ยท 0.75-1 grams/day PO divided 2-4 times daily at regular intervals ยท PO ยท divided 2-4 times daily ยท Doses are not standardized; use for general guidance only.
Routes of administration
Contraindications
- Hypersensitivity to aminoglycosides
- Intestinal obstruction (for oral use)
- Rabbits and hares (disrupts GI flora)
- Neonates (avoid oral use due to higher systemic absorption)
- Animals with a perforated tympanic membrane (eardrum)
- Concurrent use with other known ototoxic products
- Known hypersensitivity to aminoglycosides
- Pre-existing renal disease (for systemic use)
- Ruptured tympanic membrane (for otic preparations)
Adverse effects
- Nephrotoxicity (severe if given parenterally)
- Ototoxicity (irreversible, parenteral or rarely oral)
- Severe diarrhea
- Intestinal malabsorption
- GI superinfections (with chronic oral use)
- Ototoxicity (deafness)
- Vestibular toxicity (ataxia, head tilt, nystagmus)
- Local irritation or erythema at the application site
- Ototoxicity (vestibular and auditory)
- Nephrotoxicity
- Severe diarrhoea or malabsorption syndrome (oral use)
- Bacterial or fungal superinfections
- Local irritation (topical ophthalmic use)
Drug interactions
- Digoxin ยท Oral neomycin may decrease digoxin absorption. In a small subset of patients who metabolize digoxin in the GI tract, neomycin may increase serum digoxin levels. ยท moderate
- Methotrexate ยท Absorption may be reduced by oral neomycin. ยท moderate
- Ototoxic or Nephrotoxic Drugs ยท Concurrent use increases the risk of additive toxicity, even with oral neomycin, and should be done with caution.
- Penicillin VK (oral) ยท Concurrent use may cause malabsorption of the penicillin.
- Warfarin ยท Oral neomycin may decrease vitamin K absorption from the gut, potentially increasing anticoagulant effects.
- Other ototoxic drugs (e.g., loop diuretics, other aminoglycosides) ยท Increased risk of cumulative ototoxicity (deafness and vestibular dysfunction) ยท major
- Potassium ยท Decreased absorption of potassium ยท minor
- Vitamin K ยท Decreased absorption of vitamin K ยท moderate
- Furosemide ยท Synergistic ototoxicity and nephrotoxicity ยท major
Monitoring
- Clinical efficacy
- Systemic and GI adverse effects with prolonged use
- Renal function parameters (BUN, creatinine, urinalysis) if used parenterally
- Resolution of clinical signs of otitis
- Integrity of the tympanic membrane (via otoscopy)
- Hearing function and vestibular signs (head tilt, ataxia, nystagmus)
- Renal function (BUN, Creatinine, Urinalysis for casts/protein)
- Hearing and vestibular function (head tilt, nystagmus, ataxia)
- Gastrointestinal signs (diarrhoea)
Overdose
Parenteral overdosage carries a high risk of severe **nephrotoxicity** and **ototoxicity**. Oral overdosage is less likely to cause systemic toxicity unless the gut wall is compromised, but can lead to severe diarrhea and malabsorption.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.