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.
Adult: 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.
Note: 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.
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.
Pregnancy: Category C (US FDA). Crosses the placenta. Avoid use, especially during the third trimester and labor, due to potential risk of 'Gray Baby Syndrome' in the neonate from systemic exposure. Topical ophthalmic use may be considered if benefit outweighs risk, but systemic absorption should be minimized by nasolacrimal occlusion.
Driving: May cause temporary blurring of vision immediately after application. Patients should not drive or operate machinery until vision clears.
| 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 |
Same composition (Chloramphenicol (0.5% w/v)), different brands: