Makindo Medical Notes

💡 Key Clinical Insight: Neomycin is an aminoglycoside antibiotic that remains largely unabsorbed from the gut, making it useful for bowel decontamination or hepatic encephalopathy. ⚠️ Despite minimal systemic absorption, nephrotoxicity and ototoxicity can still occur, especially with prolonged use or renal impairment.

🧠 About

• Neomycin sulfate is an aminoglycoside antibiotic with poor gastrointestinal absorption.
• It acts locally in the bowel to reduce bacterial flora — lowering ammonia production and risk of infection.
• It has a narrow therapeutic index; use is now limited due to safer alternatives (e.g. rifaximin for hepatic encephalopathy).

⚙️ Mechanism of Action

• Binds irreversibly to the 30S ribosomal subunit of bacteria.
• Inhibits protein synthesis by causing misreading of mRNA.
• When taken orally, acts locally in the gut lumen to suppress ammonia-producing and pathogenic bacteria.

🎯 Indications & Typical Doses

• Pre-operative bowel sterilisation: 1 g every hour for 4 hours, then 1 g every 4 hours for 2–3 days (oral).
• Hepatic coma / encephalopathy: Up to 4 g/day in divided doses for 5–7 days to reduce intestinal ammonia-producing flora.

🔗 Interactions

• Increased nephrotoxicity or ototoxicity when used with: – Other aminoglycosides (gentamicin, amikacin) – Vancomycin – Amphotericin B – Cisplatin – Loop diuretics (e.g. furosemide).
• Always check the BNF for a full interaction list.

⚠️ Cautions

• Monitor renal function closely, especially in elderly or pre-existing renal impairment.
• Prolonged or high-dose use may still result in systemic absorption and toxicity.
• Avoid concurrent ototoxic or nephrotoxic medications.
• Adjust or avoid in hepatic coma if bowel integrity is impaired (↑ absorption risk).

🚫 Contraindications

• ❌ Myasthenia gravis — may cause neuromuscular blockade and respiratory depression.
• ❌ Hypersensitivity to aminoglycosides.

💥 Adverse Effects

• 🧏‍♂️ Ototoxicity: irreversible hearing loss or vestibular damage with cumulative exposure.
• 🩸 Nephrotoxicity: tubular damage causing rising urea and creatinine (even with partial absorption).
• 💧 GI effects: diarrhoea, steatorrhoea, and malabsorption due to mucosal injury.
• 🤢 Increased salivation and bloating.
• 💊 Contact hypersensitivity if used topically (dermatitis or eczema-like reactions).

🧾 Monitoring

💡 Teaching Tip

• Neomycin illustrates the concept of local action with systemic risk — poor absorption doesn’t mean it’s harmless.
• In hepatic encephalopathy, it reduces ammonia-producing bacteria but is now largely replaced by rifaximin due to a safer profile.
• When teaching aminoglycosides, emphasise the triad: Nephrotoxicity – Ototoxicity – Neuromuscular blockade.

📚 References

• BNF: Neomycin
• MHRA Drug Safety Update (2018): Aminoglycoside-associated ototoxicity
• Brunton LL et al. Goodman & Gilman’s The Pharmacological Basis of Therapeutics, 14th ed.