1. Clinical Overview
A topical fixed-dose antibiotic combination ointment/cream containing Polymyxin B sulfate (a polypeptide antibiotic) and Chloramphenicol (a broad-spectrum bacteriostatic antibiotic). This combination provides synergistic bactericidal activity against a wide range of Gram-positive and Gram-negative bacteria, including multi-drug resistant strains like MRSA and Pseudomonas aeruginosa, commonly used for superficial skin and eye infections in the Indian setting. It is particularly effective against mixed bacterial infections.
| Onset | Duration | Bioavailability |
|---|---|---|
| Topical: Antimicrobial action begins within minutes of application. Clinical improvement in symptoms like redness and discharge is typically observed within 24-48 hours. | Local effect persists for approximately 6-8 hours post-application, necessitating multiple daily applications as prescribed. | Negligible systemic absorption when applied to intact skin. Minimal absorption through denuded skin, wounds, or mucous membranes (e.g., conjunctiva). Chloramphenicol systemic absorption from topical use is generally <1%. |
2. Mechanism of Action
The combination exerts a dual bactericidal mechanism. Polymyxin B binds to lipopolysaccharides (LPS) in the outer membrane of Gram-negative bacteria, disrupting membrane integrity and increasing permeability, leading to cell death. Chloramphenicol inhibits bacterial protein synthesis by binding reversibly to the 50S ribosomal subunit, preventing peptide bond formation. Together, they cover a broad spectrum and can act synergistically against many organisms.
3. Indications & Uses
- Superficial bacterial infections of the skin (e.g., impetigo, folliculitis, infected wounds, minor burns)
- Bacterial conjunctivitis (as an ophthalmic ointment formulation)
- Secondary infection in dermatological conditions like eczema and ulcers
- Prophylaxis and treatment of minor cuts, abrasions, and surgical wound sites.
4. Dosage & Administration
Adult Dosage: Apply a thin layer to the affected area 2 to 4 times daily, or as directed by the physician. For ophthalmic use: Instill a small amount (approx. 1 cm ribbon) into the conjunctival sac every 3-6 hours, or as prescribed.
Administration: Clean and dry the affected area before application. Use a sterile applicator or clean hands. Wash hands before and after application. Do not cover with occlusive dressings unless advised. For eyes, avoid touching the tip of the tube to any surface to prevent contamination. Do not use for longer than the prescribed duration.
5. Side Effects
Common side effects may include:
- Local burning or stinging sensation upon application
- Mild itching or irritation
- Skin dryness or erythema at the application site.
- Transient blurring of vision (ophthalmic use).
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Other topical antibiotics (e.g., Neomycin, Bacitracin) | Potential for additive toxicity or irritation. | Moderate |
| Oral anticoagulants (Warfarin) | Chloramphenicol may inhibit metabolism of warfarin, increasing INR and bleeding risk (relevant if systemic absorption). | Major |
| Phenytoin, Phenobarbital | Chloramphenicol may increase serum levels of these drugs via metabolic inhibition. | Major |
| Sulfonylureas (e.g., Glimepiride) | Chloramphenicol may potentiate hypoglycemic effect. | Moderate |
| Neuromuscular blocking agents (e.g., Succinylcholine) | Polymyxin B may potentiate neuromuscular blockade. | Major |
7. Patient Counselling
- DO use exactly as prescribed for the full prescribed length of time.
- DO clean the affected area gently before application.
- DO wash your hands before and after applying the medicine.
- DON'T use it for longer than 7-10 days unless advised by your doctor.
- DON'T apply to large areas of broken skin without medical advice.
- DON'T share your medicine with others.
- DON'T use it if the seal is broken or the product has changed color/consistency.
8. Toxicology & Storage
Overdose: Topical overdose is unlikely to cause systemic toxicity unless applied excessively over very large body surface areas. Symptoms would reflect Chloramphenicol toxicity (bone marrow depression, Gray Baby Syndrome in infants) and Polymyxin B toxicity (neurotoxicity - dizziness, paresthesia; nephrotoxicity).
Storage: Store at room temperature (15-25°C), in a cool, dry place. Protect from light and moisture. Do not freeze. Keep the tube tightly closed. Keep out of reach of children and pets. Do not use after the expiry date printed on the packaging.