1. Clinical Overview
Chloramphenicol is a broad-spectrum bacteriostatic antibiotic originally derived from *Streptomyces venezuelae*. The 0.5% w/v formulation is primarily used as a topical ophthalmic solution for the treatment of superficial bacterial infections of the eye. It inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit. In India, it is a widely available, cost-effective first-line agent for bacterial conjunctivitis, though its systemic use is severely restricted due to the risk of fatal aplastic anemia.
| Onset | Duration | Bioavailability |
|---|---|---|
| Therapeutic concentrations in ocular tissues are achieved within 30 minutes of topical application. | Approximately 4 to 6 hours per application, necessitating frequent dosing (e.g., every 3-6 hours). | Negligible systemic absorption following topical ophthalmic application in a non-inflamed eye. Systemic bioavailability from oral administration is 75-90%. |
2. Mechanism of Action
Chloramphenicol binds reversibly to the 50S subunit of the bacterial 70S ribosome. It inhibits the peptidyl transferase activity, thereby preventing the transfer of the growing peptide chain to the next aminoacyl-tRNA. This action blocks the formation of peptide bonds, leading to inhibition of bacterial protein synthesis.
3. Indications & Uses
- Acute Bacterial Conjunctivitis
- Bacterial Keratitis (superficial)
- Bacterial Blepharitis
- As prophylaxis following corneal abrasion (short-term)
4. Dosage & Administration
Adult Dosage: Ophthalmic Solution (0.5%): Instill 1 to 2 drops into the affected eye(s) every 3 to 6 hours. In severe infections, may be used hourly initially, tapering frequency as infection improves.
Administration: 1. Wash hands before use. 2. Tilt head back, pull lower eyelid down to form a pouch. 3. Instill prescribed drops without touching the dropper tip to eye, eyelid, or any surface. 4. Close eye gently for 1-2 minutes, applying gentle pressure to the nasolacrimal duct (inner corner of eye) to minimize systemic absorption. 5. 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
- Blurred vision temporarily after application
- Mild ocular irritation/itching
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Oral Anticoagulants (Warfarin, Acenocoumarol) | Chloramphenicol (systemic) inhibits hepatic metabolism, potentiating anticoagulant effect, increasing INR and bleeding risk. | Major |
| Phenytoin, Phenobarbital | Chloramphenicol (systemic) inhibits metabolism, increasing phenytoin/phenobarbital levels and risk of toxicity. Conversely, these drugs may decrease chloramphenicol levels. | Major |
| Sulfonylureas (e.g., Glipizide, Glyburide) | Chloramphenicol (systemic) may potentiate hypoglycemic effect. | Moderate |
| Vitamin B12, Folic Acid, Iron Supplements | Chloramphenicol (systemic) may antagonize the hematopoietic response to these agents. | Moderate |
| Other Myelosuppressive Drugs (e.g., Chemotherapy, Zidovudine, Clozapine) | Additive risk of bone marrow toxicity. | Major |
7. Patient Counselling
- DO wash hands before and after use.
- DO apply gentle pressure to the inner corner of the eye (nasolacrimal duct) for 1-2 minutes after instillation to reduce systemic absorption.
- DO complete the full course as prescribed, even if symptoms improve.
- DO NOT touch the dropper tip to any surface to avoid contamination.
- DO NOT wear contact lenses while having an active infection or while using this medication unless approved by your doctor.
- DO NOT share your eye drops with others.
8. Toxicology & Storage
Overdose: Topical: Unlikely to cause systemic overdose. Accidental oral ingestion of ophthalmic solution may cause: Nausea, vomiting, diarrhea, unpleasant taste. Systemic overdose: 'Gray Baby Syndrome' in infants, bone marrow suppression, cardiovascular collapse.
Storage: Store at room temperature (15-25°C). Protect from light. Keep the bottle tightly closed. Do not freeze. Keep out of reach of children.