Introduction
Neomycin is an aminoglycoside antibiotic derived from Streptomyces fradiae. First isolated in 1949, it has been widely used for decades primarily as a topical preparation due to its significant systemic toxicity when administered orally or parenterally. Neomycin demonstrates bactericidal activity against a broad spectrum of Gram-negative and some Gram-positive organisms, though its clinical utility is now largely limited to topical applications and selective oral use for hepatic encephalopathy prophylaxis due to its poor systemic absorption and toxicity profile.
Mechanism of Action
Neomycin exerts its bactericidal effect by binding irreversibly to the 30S ribosomal subunit of susceptible bacteria. This binding inhibits protein synthesis in two primary ways: 1) it interferes with the initiation complex between mRNA and the 30S subunit, and 2) it causes misreading of the mRNA code, leading to incorporation of incorrect amino acids into the growing polypeptide chain. The resultant production of nonfunctional proteins ultimately leads to bacterial cell death.
Indications
FDA-approved indications:- Hepatic encephalopathy (oral administration)
- Topical infections caused by susceptible organisms (skin infections, burns, wounds)
- Preoperative bowel sterilization (in combination with other agents)
- Ophthalmic infections (solution/ointment)
- As part of selective digestive decontamination regimens
- Topical treatment for otitis externa
Dosage and Administration
Oral administration (hepatic encephalopathy):- Adults: 1-3 g every 6 hours for 5-6 days
- Maximum daily dose: 12 g
- Apply 1-3 times daily to affected area
- Ophthalmic: 1-2 drops in affected eye every 3-4 hours
- Renal impairment: Dose adjustment required for oral administration
- Hepatic impairment: No specific dosage adjustment needed
- Pediatrics: Safety and efficacy not established for oral administration
- Elderly: Increased risk of nephrotoxicity and ototoxicity
Pharmacokinetics
Absorption: Poorly absorbed from gastrointestinal tract (<3% of oral dose). Minimal systemic absorption from intact skin, but increased absorption from damaged skin, burns, or large surface areas. Distribution: Poor tissue penetration. Does not cross the blood-brain barrier significantly. Volume of distribution approximately 0.25 L/kg. Metabolism: Not metabolized significantly. Elimination: Primarily excreted unchanged in feces (>97% of oral dose). Renal excretion of absorbed drug with half-life of 2-3 hours in patients with normal renal function.Contraindications
- Hypersensitivity to neomycin or other aminoglycosides
- Intestinal obstruction (oral administration)
- Myasthenia gravis
- History of ototoxicity from aminoglycosides
- Topical use in deep or puncture wounds, animal bites, or serious burns without medical supervision
Warnings and Precautions
Boxed Warning: Systemic absorption possible with topical use on large areas, denuded skin, or burns, which may lead to nephrotoxicity, ototoxicity, and neuromuscular blockade. Additional precautions:- Monitor for superinfection with nonsusceptible organisms
- Use with caution in patients with renal impairment
- Avoid prolonged use (>7 days) due to potential for sensitization
- Cross-sensitivity with other aminoglycosides may occur
- Risk of neuromuscular blockade, especially in patients with neuromuscular disorders
Drug Interactions
- Other ototoxic drugs (vancomycin, loop diuretics, cisplatin): Increased risk of ototoxicity
- Other nephrotoxic drugs (NSAIDs, contrast media, amphotericin B): Increased risk of nephrotoxicity
- Neuromuscular blocking agents: Potentiation of neuromuscular blockade
- Oral anticoagulants: Possible potentiation of anticoagulant effect
- Digoxin, methotrexate: Possible decreased absorption of these drugs
Adverse Effects
Common (topical use):- Contact dermatitis
- Skin irritation
- Pruritus
- Rash
- Nephrotoxicity (elevated BUN, creatinine)
- Ototoxicity (tinnitus, hearing loss, vertigo)
- Neuromuscular blockade
- Superinfections
- Allergic reactions including anaphylaxis
Monitoring Parameters
- Renal function: BUN, serum creatinine (with prolonged use or large surface area application)
- Auditory function: Baseline and periodic audiograms with prolonged use
- Vestibular function: Assessment for dizziness, vertigo, nystagmus
- Therapeutic response: Resolution of infection
- Signs of hypersensitivity: Rash, itching, swelling
Patient Education
- Use exactly as prescribed; do not exceed recommended duration
- For topical use: Cleanse area before application; use sterile dressing if indicated
- Report any hearing changes, dizziness, ringing in ears, or decreased urine output immediately
- Complete full course of therapy even if symptoms improve
- Do not use on large areas of skin without medical supervision
- Store at room temperature away from moisture
- Discard any unused medication after treatment course completed
References
1. Gilbert DN, Chambers HF, Eliopoulos GM, et al. The Sanford Guide to Antimicrobial Therapy. 52nd ed.; 2022. 2. Neomycin sulfate [package insert]. Philadelphia, PA: X-Gen Pharmaceuticals; 2021. 3. Drew RH, Gallagher JC. Aminoglycosides. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Elsevier; 2020. 4. Lexicomp Online. Neomycin. Wolters Kluwer Clinical Drug Information; 2023. 5. FDA-approved labeling for neomycin-containing products. Accessible via Drugs@FDA. 6. Rybak MJ, Le J, Lodise TP, et al. Therapeutic monitoring of vancomycin for serious methicillin-resistant Staphylococcus aureus infections: A revised consensus guideline and review by the American Society of Health-System Pharmacists, the Infectious Diseases Society of America, the Pediatric Infectious Diseases Society, and the Society of Infectious Diseases Pharmacists. Am J Health Syst Pharm. 2020;77(11):835-864.