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.
กลไกการออกฤทธิ์: 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** → causes misreading of mRNA → inhibits protein synthesis → leads to rapid bacterial cell death.
ขนาดยาตามชนิดสัตว์
- Hepatic encephalopathy · 22 mg/kg q8h PO · PO · q8h
- Hepatic encephalopathy · 20 mg/kg PO q8-12h · PO · q8-12h · Used with or without lactulose.
- Hepatic encephalopathy (stable animals) · 20 mg/kg PO q12h · PO · q12h · Avoid if evidence of intestinal bleeding, ulcerations, or renal failure.
- Campylobacteriosis · 20 mg/kg PO q12h · PO · q12h
- Systemic therapy · 3.5 mg/kg IV , IM or SC q8h · IV/IM/SC · q8h · Caution: Very nephrotoxic.
- Susceptible enteral infections (Young pigs) · 0.75-1 grams/day, PO divided 2-4 times daily at regular intervals · PO · divided 2-4 times daily · Doses are not standardized; use for general guidance only.
- Susceptible enteral infections · 7-12 mg/kg, PO q12h · PO · q12h
- Susceptible enteric infections · 10-20 mg/kg, PO twice to four times daily · PO · q6-12h
- Susceptible enteral infections (Lambs) · 0.75-1 grams/day PO divided 2-4 times daily at regular intervals · PO · divided 2-4 times daily · Doses are not standardized; use for general guidance only.
วิธีการให้ยา
ข้อห้ามใช้
- 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)
อาการไม่พึงประสงค์
- 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)
อันตรกิริยาระหว่างยา
- Digoxin · 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. · moderate
- Methotrexate · Absorption may be reduced by oral neomycin. · moderate
- Ototoxic or Nephrotoxic Drugs · Concurrent use increases the risk of additive toxicity, even with oral neomycin, and should be done with caution.
- Penicillin VK (oral) · Concurrent use may cause malabsorption of the penicillin.
- Warfarin · Oral neomycin may decrease vitamin K absorption from the gut, potentially increasing anticoagulant effects.
- Other ototoxic drugs (e.g., loop diuretics, other aminoglycosides) · Increased risk of cumulative ototoxicity (deafness and vestibular dysfunction) · major
- Potassium · Decreased absorption of potassium · minor
- Vitamin K · Decreased absorption of vitamin K · moderate
- Furosemide · Synergistic ototoxicity and nephrotoxicity · major
การติดตาม
- 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)
การได้รับยาเกินขนาด
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.
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