Chloramphenicol is a broad-spectrum bacteriostatic antibiotic, originally derived from *Streptomyces venezuelae*, now produced synthetically. The 1% w/w topical formulation (typically as an eye/ear ointment or solution) is a mainstay in Indian ophthalmology and dermatology for treating superficial bacterial infections. It inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit. Its use is now largely restricted to topical applications due to the risk of serious systemic adverse effects like aplastic anemia and gray baby syndrome.
Adult: **Eye Ointment/Solution (1%):** Apply a ~1 cm ribbon of ointment or 1-2 drops into the conjunctival sac(s) every 3-6 hours, depending on severity. Frequency may be reduced after 48 hours of improvement. **Ear Ointment/Drops (1%):** Fill the ear canal with ointment or instill 2-3 drops 2-3 times daily. **Topical Skin:** Apply a thin layer to affected area 2-3 times daily.
Note: 1. **For Eyes:** Wash hands. Tilt head back. Gently pull lower eyelid down to form a pouch. Apply ointment/drops without touching the tip to eye or any surface. Close eye for 1-2 minutes. Apply pressure to the nasolacrimal duct (inner corner of eye) for 1 minute to minimize systemic absorption. 2. **For Ears:** Clean and dry the ear canal gently. Warm the drops/ointment by holding the container in hand for a few minutes. Lie on side. Instill drops/ointment. Remain on side for 5 minutes. 3. **For Skin:** Clean and dry area. Apply a thin layer. May cover with a sterile dressing if needed. 4. Do not share medication. Discard eye/ear drops 4 weeks after opening unless otherwise stated.
Chloramphenicol exerts its bacteriostatic effect by reversibly binding to the 50S subunit of the bacterial 70S ribosome. This binding inhibits the peptidyl transferase activity, preventing the transfer of the growing peptide chain from the P-site to the A-site tRNA. Consequently, it blocks the formation of peptide bonds, halting bacterial protein synthesis.
Pregnancy: **Category C (US FDA).** Chloramphenicol crosses the placenta. Topical use at recommended doses is generally considered low risk due to minimal systemic absorption. However, systemic use near term or during labor is associated with "Gray Baby Syndrome." Use only if clearly needed and for the shortest duration possible.
Driving: Ointment formulations can cause temporary blurring of vision. Patients should not drive or operate machinery until vision clears, usually 10-15 minutes after application.
| **Phenobarbital, Phenytoin, Rifampicin** | Induce hepatic enzymes, potentially increasing chloramphenicol metabolism and reducing its efficacy if absorbed systemically. Conversely, chloramphenicol can inhibit metabolism of these drugs, increasing their toxicity. | Moderate |
| **Warfarin, Acenocoumarol** | Chloramphenicol (if absorbed) inhibits CYP2C9, potentiating anticoagulant effect, increasing risk of bleeding. | Major |
| **Sulfonylureas (e.g., Glibenclamide)** | Chloramphenicol (if absorbed) can inhibit their metabolism, leading to enhanced hypoglycemic effect. | Moderate |
| **Vitamin B12, Iron Supplements** | Chloramphenicol (systemic) can antagonize the hematopoietic response to these agents. | Moderate |
| **Other Myelosuppressive drugs (e.g., Chemotherapy, Zidovudine, Clozapine)** | Additive risk of bone marrow toxicity. | Major |
| **Macrolides (Erythromycin), Lincosamides (Clindamycin)** | Competitive antagonism at ribosomal binding site; may reduce antibacterial efficacy. Avoid concurrent topical use in same field. | Moderate |
Same composition (Chloramphenicol (1% w/w)), different brands: