1. Clinical Overview
A sterile, topical ophthalmic solution combining two bactericidal antibiotics with complementary mechanisms of action. Polymyxin B is a cationic polypeptide antibiotic effective against Gram-negative bacteria, particularly Pseudomonas aeruginosa. Chloramphenicol is a broad-spectrum bacteriostatic antibiotic effective against a wide range of Gram-positive and Gram-negative bacteria, including Haemophilus influenzae and Streptococcus pneumoniae. This combination provides synergistic coverage for superficial ocular infections, particularly in the Indian context where bacterial conjunctivitis is common and often polymicrobial.
| Onset | Duration | Bioavailability |
|---|---|---|
| Therapeutic concentrations are achieved at the ocular surface within minutes of topical application. | Approximately 4-6 hours per instillation, necessitating multiple daily doses. | Negligible systemic absorption following topical ophthalmic administration. Primarily acts locally at the site of infection. |
2. Mechanism of Action
The combination exerts a dual bactericidal/bacteriostatic action. Polymyxin B binds to the lipopolysaccharide (LPS) and phospholipids in the outer cell membrane of Gram-negative bacteria, acting as a cationic detergent that disrupts membrane integrity, leading to leakage of intracellular contents and cell death. Chloramphenicol inhibits bacterial protein synthesis by binding reversibly to the 50S subunit of the bacterial ribosome, preventing peptide bond formation. This combination is effective against a broad spectrum of ocular pathogens.
3. Indications & Uses
- Acute Bacterial Conjunctivitis
- Bacterial Blepharitis
- Bacterial Keratitis (superficial)
- Prophylaxis post-ocular surgery or corneal abrasion
4. Dosage & Administration
Adult Dosage: One to two drops in the affected eye(s) every 4 to 6 hours. In severe infections, may be used hourly initially, tapering as infection improves.
Administration: 1. Wash hands. 2. Tilt head back. 3. Gently pull lower eyelid to form a pouch. 4. Instill prescribed drops without touching the dropper tip to eye or any surface. 5. Close eyes gently for 1-2 minutes. 6. Apply gentle pressure to the nasolacrimal duct (inner corner of eye) for 1 minute to minimize systemic absorption. 7. Wait at least 5-10 minutes before instilling any other eye medication.
5. Side Effects
Common side effects may include:
- Transient burning or stinging upon instillation
- Mild ocular irritation
- Blurred vision temporarily
- Itching or redness
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Other Myelosuppressive drugs (e.g., Chemotherapy, Azathioprine) | Increased risk of bone marrow toxicity. | Major |
| Vitamin B12, Folic Acid, Iron supplements | Chloramphenicol may antagonize the hematinic response. | Moderate |
| Penicillins, Cephalosporins | Chloramphenicol, being bacteriostatic, may antagonize the bactericidal action of these drugs in systemic infections. Relevance topical is low. | Moderate |
| Paracetamol (Acetaminophen) | Increased risk of Chloramphenicol toxicity (prolonged half-life) with systemic use. | Moderate |
| Warfarin | Chloramphenicol may inhibit metabolism, increasing anticoagulant effect. | Major |
| Phenytoin, Phenobarbital | Altered metabolism of Chloramphenicol. | Moderate |
7. Patient Counselling
- DO wash hands before and after use.
- DO complete the full course as prescribed, even if symptoms improve.
- DO wait at least 5-10 minutes between different eye drops.
- DO NOT touch the dropper tip to your eye, fingers, or any surface.
- DO NOT wear contact lenses while having an infection or using this medication.
- DO NOT share your eye drops with others.
- DO NOT use leftover medication for a new infection.
8. Toxicology & Storage
Overdose: Topical overdose is unlikely to cause systemic toxicity. Accidental ingestion may cause: Nausea, vomiting, diarrhea, bone marrow depression (Chloramphenicol), neurotoxicity (paresthesia, ataxia - Polymyxin B), nephrotoxicity (Polymyxin B). In infants, Gray Baby Syndrome: vomiting, refusal to feed, abdominal distension, cyanosis, vasomotor collapse, hypothermia.
Storage: Store below 25°C. Protect from light. Keep the bottle tightly closed. Do not freeze. Keep out of reach of children. Discard the bottle 4 weeks after opening (write opening date on label). Do not use if the solution is discolored or contains particles.