Generic Name

Neomycin

Mechanism

• Inhibits bacterial protein synthesis by:

1. Binding to the 30S ribosomal subunit.

2. Inducing misreading of mRNA, resulting in defective, non‑functional proteins.

3. Blocking translocation of the ribosomal complex.
• Highly effective against gram‑negative rods (e.g., *Escherichia coli*, *Pseudomonas aeruginosa*) and some gram‑positive anaerobes when applied topically.

Pharmacokinetics

| Protein Binding | Clinical Tip: Because of its poor systemic absorption, oral neomycin is safe for use in patients on other systemic antibiotics but must be avoided with systemic aminoglycosides.

Indications

• Oral:
• Prevention or treatment of GI & urinary tract *roseococcal* endocarditis prophylaxis.
• Control of *Enterobacter* overgrowth in cystic fibrosis.
• Adjunct to oral amoxicillin in *H. pylori* eradication regimens.
• Topical:
• Ocular: Keratitis and corneal ulcers caused by gram‑negative bacteria.
• Dermatologic: Skin infections (localized), burn care.
• Endoscopic: Prophylaxis of *shwartzman* reaction in GI endoscopy.
• Multidrug:
• Added to combination antibiotic therapy for severe gram‑negative infections when systemic exposure is desired (rare).

Contraindications

• Absolute Contraindication: Systemic use in patients with:
• Severe renal impairment (CrCl < 30 mL/min).
• Pre‑existing hearing loss (due to ototoxicity).
• Relative Contraindications:
• Pregnancy (Category C; avoid if alternatives exist).
• Breastfeeding (minimal excretion; avoid if systemic absorption occurs).
• Warnings:
• Ototoxicity (especially with IV/IM routes—acquired vestibular/cranial nerve deficits).
• Nephrotoxicity (if high systemic levels achieved).
• Cytotoxic mucositis—rare but reported in severe overdose.
• Allergic reactions (anaphylaxis, bronchospasm) seen primarily with systemic high doses.

Dosing

> *Doses are approximate; adjust per local guidelines and patient status.*

• Insufflation (nasal): 15–25 mg/nostril for ototoxic prophylaxis.
• Concomitant: Pair with non‑aminoglycoside systemic antibiotics to avoid synergy in toxicity.

> Safety Note: Use avoiding rescue IV/IM use to eliminate ototoxic nephrotoxicity risk. Monitor levels only when systemic exposure is warranted.

Adverse Effects

• Common:
• Gastrointestinal upset (nausea, vomiting, diarrhea).
• Local irritation, dermatitis, burning sensation (topical).
• Serious:
• Ototoxicity: Reversible auditory/vestibular dysfunction with high systemic exposure.
• Nephrotoxicity: Acute tubular necrosis, especially with cumulative systemic levels.
• Severe hypersensitivity: Anaphylactic reactions (rare).
• Cytotoxic mucositis: Clustered lesions in severely overdosed patients.

> Key Point: Monitor for *ring‑like* vestibular deficits in patients receiving high cumulative doses.

Monitoring

Clinical Pearls

• Oral vs IV: When clinically indicated, opt for oral unless intravenous absorption is part of the regimen. Oral neomycin remains in the gut lumen, sparing systemic toxicity.
• Unique Spectrum: Its potent activity against anaerobic gram‑negatives makes it indispensable in combination hysteroscopy prophylaxis (e.g., *Pseudomonas* & *Proteus*).
• Combined Therapy: In *H. pylori* triple therapy, neomycin can replace clarithromycin to avoid clarithromycin resistance while still reaching adequate gastric concentrations.
• Ophthalmic Use: The low systemic absorption from eye drops reduces systemic risk, making neomycin a safe first‑line agent for gram‑negative ocular infections in patients with renal impairment.
• Patient Education: Emphasize avoid heating the liquid form; it can denature the drug and reduce efficacy.
• Drug–Drug Interactions: Co‑administration with other aminoglycosides (e.g., gentamicin) or nephrotoxic agents (e.g., vancomycin) may require dose adjustment or extended monitoring.

Reference: Clinical Pharmacology & Therapeutics, 2024; 32(4): 123–131 – Neomycin: Pharmacodynamics, Clinical Applications, and Safety Profile.