Usage
Neomycin + Polymyxin B is a combination antibiotic primarily used topically for the prevention and treatment of superficial bacterial infections of the skin, eyes, and ears. It is effective against a broad spectrum of gram-positive and gram-negative bacteria. Its pharmacological classification is antibiotic. The combination works by inhibiting bacterial protein synthesis (neomycin) and increasing bacterial cell membrane permeability (polymyxin B), leading to bacterial death.
Alternate Names
This combination is often referred to as neomycin/polymyxin B. Several brand names exist depending on the formulation and manufacturer, including Neosporin, AK-Trol, Maxitrol, NeoPolyDex, Ocu-Trol, and Poly-Dex. Brand names for otic formulations include Cort-Biotic, Cortisporin, Cortomycin, Oti-Sone, and Pediotic.
How It Works
Pharmacodynamics: Neomycin, an aminoglycoside antibiotic, interferes with bacterial protein synthesis by binding to the 30S ribosomal subunit. Polymyxin B, a polypeptide antibiotic, disrupts the bacterial cell membrane by binding to phospholipids, leading to increased permeability and leakage of intracellular contents. The combination exhibits synergistic bactericidal activity.
Pharmacokinetics: When used topically, systemic absorption is generally minimal. However, absorption can increase with application to large areas of damaged skin or with prolonged use. Absorption can also occur from mucous membranes, particularly in the eye. Minimal amounts are absorbed into the eye following topical ophthalmic administration. Some degree of absorption may occur through inflamed or damaged skin. Neomycin is mainly excreted unchanged by the kidneys. Polymyxin B is also primarily excreted renally, albeit with limited clearance.
Mode of Action: Neomycin acts by binding to bacterial ribosomal RNA, inhibiting protein synthesis and causing misreading of the genetic code. Polymyxin B binds to cell membrane phospholipids, disrupting membrane integrity and function.
Receptor Binding, Enzyme Inhibition, or Neurotransmitter Modulation: Neomycin targets bacterial ribosomes. Polymyxin B targets bacterial cell membranes. Neither drug significantly interacts with human receptors, enzymes, or neurotransmitters when used topically.
Elimination Pathways: When absorbed systemically, both neomycin and polymyxin B are primarily excreted by the kidneys.
Dosage
Standard Dosage
Adults: Topical application to the affected area 1 to 3 times daily. Ophthalmic solutions: 1-2 drops in the affected eye(s) every 4 hours for 7-10 days. Ophthalmic ointments: Apply a small amount (approximately 1/2 inch ribbon) to the affected eye(s) 1 to 3 times a day. Otic solutions: 4-10 drops in affected ear(s) every 6-8 hours.
Special Cases:
- Elderly Patients: Use with caution due to potential for decreased renal function. Monitor renal function.
- Patients with Renal Impairment: Dose adjustment may be necessary. Monitor renal function and serum neomycin/polymyxin B levels.
- Patients with Hepatic Dysfunction: No specific dose adjustments are typically required for topical use.
- Patients with Comorbid Conditions: Exercise caution in patients with skin conditions that may enhance systemic absorption (e.g., burns, open wounds).
Clinical Use Cases
This combination medication is not typically used for systemic indications. It’s mainly used topically for localized infections. Dosage in clinical settings like those described would be determined by the specific infection being treated and guided by other antibiotics that achieve systemic concentrations.
Dosage Adjustments
Dose adjustments are primarily based on renal function. Therapeutic drug monitoring (serum neomycin/polymyxin B levels) may be considered in patients with renal impairment or with extensive topical application.
Side Effects
Common Side Effects
- Local irritation (burning, stinging, itching, redness)
- Allergic contact dermatitis
Rare but Serious Side Effects
- Ototoxicity (hearing loss, tinnitus) - primarily with systemic absorption
- Nephrotoxicity (kidney damage) - primarily with systemic absorption
- Anaphylaxis (rare but serious allergic reaction)
Long-Term Effects
Prolonged topical use, especially in the eye, may increase the risk of:
- Glaucoma
- Cataracts
- Secondary ocular infections (including fungal infections)
- Thinning of the cornea or sclera
Adverse Drug Reactions (ADR)
Severe allergic reactions (anaphylaxis) require immediate medical intervention.
Contraindications
- Hypersensitivity to neomycin, polymyxin B, or any component of the formulation.
- Viral infections of the eye (e.g., herpes simplex keratitis).
- Fungal infections of the eye or ear.
- Mycobacterial infection of the eye.
- Perforated tympanic membrane (for otic formulations).
Drug Interactions
- Other aminoglycosides (increased risk of nephrotoxicity and ototoxicity).
- Neuromuscular blocking agents (increased risk of respiratory depression).
- Certain other nephrotoxic drugs (increased risk of kidney damage).
- Oral microbiota (decreased efficacy of the microbiota).
Pregnancy and Breastfeeding
- Pregnancy Safety Category: C (Ophthalmic)
- Fetal risk cannot be ruled out. Use only if the potential benefit outweighs the risk.
- It is unknown if this drug is excreted in breast milk. Use with caution during breastfeeding.
Drug Profile Summary
- Mechanism of Action: Neomycin inhibits bacterial protein synthesis; Polymyxin B disrupts bacterial cell membranes.
- Side Effects: Local irritation, allergic contact dermatitis, rarely ototoxicity, nephrotoxicity, and anaphylaxis.
- Contraindications: Hypersensitivity, viral eye infections, fungal eye/ear infections, mycobacterial eye infections, perforated eardrum.
- Drug Interactions: Aminoglycosides, neuromuscular blockers, nephrotoxic drugs, oral microbiota.
- Pregnancy & Breastfeeding: Use with caution. Category C.
- Dosage: Varies depending on formulation and site of infection. See detailed dosage section.
- Monitoring Parameters: Renal function if systemic absorption is suspected, intraocular pressure with prolonged ophthalmic use.
Popular Combinations
- Neomycin + Polymyxin B + Bacitracin: Topical antibiotic combination for skin infections.
- Neomycin + Polymyxin B + Hydrocortisone: Topical/Otic antibiotic and corticosteroid combination for ear and eye infections.
- Neomycin + Polymyxin B + Dexamethasone: Ophthalmic antibiotic and corticosteroid combination for eye infections and inflammation.
- Neomycin + Polymyxin B + Gramicidin: Ophthalmic antibiotic combination for eye infections.
Precautions
- General Precautions: Perform pre-screening for allergies. Avoid contact with eyes (unless ophthalmic formulation). Do not use for longer than prescribed.
- Specific Populations: See “Dosage - Special Cases.”
- Lifestyle Considerations: No specific lifestyle considerations.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Neomycin + Polymyxin B?
A: Dosage varies by formulation and indication. See detailed dosage information above.
Q2: Can Neomycin + Polymyxin B be used for inner ear infections?
A: No, this combination is indicated for outer ear infections (otitis externa). Inner ear infections require systemic antibiotics.
Q3: Can I use this medication if I am allergic to other antibiotics?
A: Inform your doctor about any drug allergies, especially to aminoglycosides. Cross-reactivity is possible.
Q4: Can this medication be used during pregnancy or while breastfeeding?
A: Use with caution during pregnancy and breastfeeding. Consult with a physician to assess the risk/benefit ratio.
Q5: What should I do if my symptoms don’t improve after a few days?
A: Consult your physician. A different treatment or further investigation may be needed.
A: No. Remove contact lenses before application and wait at least 15 minutes before reinserting them.
Q7: Can Neomycin + Polymyxin B be used on open wounds?
A: Use with caution on open wounds. Extensive use on large open wounds may increase the risk of systemic absorption and toxicity.
Q8: What are the signs of an allergic reaction to this medication?
A: Signs of an allergic reaction include itching, rash, hives, swelling of the face, lips, or tongue, and difficulty breathing. Seek immediate medical attention if these occur.
Q9: How should this medication be stored?
A: Store at room temperature (15-25°C), protect from light, and keep out of reach of children.
