Neomycin: An Aminoglycoside Antibiotic with Specific Clinical Applications
Neomycin is an aminoglycoside antibiotic primarily used for suppression of intestinal bacteria before surgery, treatment of hepatic encephalopathy, and as a topical antibiotic, though it has significant limitations due to toxicity concerns. 1
Pharmacology and Mechanism of Action
Neomycin is an antibiotic derived from the actinomycete Streptomyces fradiae. It works by inhibiting protein synthesis in susceptible bacterial cells, making it bactericidal in nature. 2
Key pharmacological properties include:
- Poor absorption from the normal gastrointestinal tract (approximately 97% eliminated unchanged in feces)
- Rapid suppression of most intestinal bacteria following oral administration, with effects persisting for 48-72 hours
- Primary activity against gram-negative bacilli with some activity against gram-positive organisms
- Specific activity against Escherichia coli and Klebsiella-Enterobacter groups
- No activity against anaerobic bowel flora 2
Clinical Applications
1. Hepatic Encephalopathy
- Used as an alternative choice for treatment of overt hepatic encephalopathy (Grade II-1, B, 2) 3
- Works by reducing ammonia-forming bacteria in the intestinal tract 1
- Often used when other treatments have failed or are contraindicated
2. Preoperative Bowel Preparation
- Used as adjunctive therapy for preoperative suppression of intestinal bacteria 1
- Helps reduce bacterial load before gastrointestinal surgery
3. Irritable Bowel Syndrome (IBS)
- May be used in combination therapy for specific IBS cases
- Combination of rifaximin and neomycin (85% clinical response) is more effective than neomycin alone (63%) or rifaximin alone (56%) in treating methane-positive IBS patients 4
- Used in late-onset diarrhea after irinotecan therapy (500 mg bid po) 3
4. Decolonization of Multidrug-Resistant Bacteria
- Has been studied in combination with colistin for temporary suppression of multidrug-resistant Enterobacteriaceae carriage 3
Toxicity and Safety Concerns
Neomycin has significant toxicity concerns that limit its use:
Ototoxicity: Can cause permanent hearing loss, particularly with prolonged use or systemic absorption 5
Nephrotoxicity: Can cause renal damage, which is usually reversible if detected early 5
Hypersensitivity: Approximately 5-15% of patients with chronic external otitis may develop hypersensitivity to neomycin 1
Systemic Absorption: Even with oral administration, some systemic absorption can occur, posing serious risks including neurotoxicity 1
Dosing and Administration
For oral administration:
- Available as 500 mg tablets (equivalent to 350 mg neomycin base) 2
- Typical dosing varies by indication:
Special Populations and Precautions
- Elderly patients: Higher risk of toxicity, requiring careful monitoring of renal function and hearing 1
- Renal impairment: Requires dose adjustment and careful monitoring 1
- Pregnancy: Should be used with caution due to potential risks 1
Drug Interactions
Neomycin may interact with other antibiotics:
- Synergistic effects observed when combined with peptide antibiotics (polymyxin, gramicidin, and bacitracin)
- No synergy observed when combined with beta-lactams (ampicillin, procaine penicillin) 6
Resistance Concerns
Like other aminoglycosides, bacterial resistance to neomycin is a growing concern, leading to research into modified versions of the drug to overcome resistance mechanisms 7. Careful and appropriate use is essential to minimize the development of resistance.
Alternatives
For most indications, neomycin is not a first-line treatment. Alternative treatments with better safety profiles are often preferred, particularly for long-term use.
For example, in treating hepatic encephalopathy: