Neomycin 💊
💡 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
| Parameter | Baseline | Ongoing |
|---|
| Renal function (U&E, eGFR) | ✔️ | ✔️ Daily if prolonged use |
| Auditory function | ✔️ Baseline audiometry if feasible | ✔️ If tinnitus or hearing loss develops |
| Stool frequency and consistency | — | Monitor for steatorrhoea or diarrhoea |
💡 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.
