1. Clinical Overview
Chloramphenicol is a broad-spectrum bacteriostatic antibiotic originally derived from *Streptomyces venezuelae*. It is a potent inhibitor of bacterial protein synthesis. Due to its association with serious and potentially fatal hematological toxicities (aplastic anemia, gray baby syndrome), its systemic use is now highly restricted in India and globally. It is primarily reserved for severe, life-threatening infections where safer alternatives are ineffective or contraindicated. Its topical use (ophthalmic, otic) remains common and is considered relatively safe.
| Onset | Duration | Bioavailability |
|---|---|---|
| Oral/IV: Peak serum concentrations reached in 1-3 hours. Topical (Ophthalmic): Onset of action within hours. | Approximately 4-8 hours, necessitating multiple daily doses for systemic therapy. | Oral: 75-90% (well absorbed). IV: 100% (bioequivalent). |
2. Mechanism of Action
Chloramphenicol binds reversibly to the 50S subunit of the bacterial 70S ribosome. This binding inhibits the peptidyl transferase step of protein synthesis, preventing the transfer of the growing peptide chain to the newly attached aminoacyl-tRNA. This results in bacteriostatic inhibition of bacterial growth.
3. Indications & Uses
- Severe Typhoid Fever (Salmonella Typhi) resistant to fluoroquinolones and 3rd gen cephalosporins
- Bacterial Meningitis (as an alternative in penicillin/cephalosporin-allergic patients, especially for H. influenzae, N. meningitidis, S. pneumoniae)
- Rickettsial infections (e.g., Scrub typhus, Rocky Mountain spotted fever) where tetracyclines are contraindicated
- Topical: Bacterial Conjunctivitis, Bacterial Keratitis, External Otitis (Otitis Externa)
4. Dosage & Administration
Adult Dosage: Systemic (Severe infections): 50 mg/kg/day in divided doses every 6 hours (IV/Oral). Max: 4 g/day. Typhoid Fever: 500 mg every 6 hours for 14 days. Topical (Eye): 1-2 drops in affected eye(s) every 2-6 hours. Ointment: Apply small amount 3-4 times daily.
Administration: Oral: Can be taken with or without food. IV: Administer as a slow intravenous infusion over 15-30 minutes. Topical Ophthalmic: Wash hands, avoid touching dropper tip, apply pressure to lacrimal sac (nasolacrimal duct) for 1 minute to minimize systemic absorption. Do not share eye/ear drops.
5. Side Effects
Common side effects may include:
- Nausea, vomiting, diarrhea
- Bitter or metallic taste
- Headache, mild depression
- Topical: Transient stinging/burning, blurred vision (ophthalmic)
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Warfarin, Acenocoumarol | Chloramphenicol inhibits metabolism, increasing anticoagulant effect and risk of bleeding. | Major |
| Phenytoin, Phenobarbital | Chloramphenicol inhibits metabolism, increasing phenytoin/phenobarbital levels (toxicity). Conversely, these drugs may decrease chloramphenicol levels. | Major |
| Sulfonylureas (Glibenclamide) | Increased hypoglycemic effect. | Moderate |
| Vitamin B12, Folic Acid, Iron | Chloramphenicol antagonizes the hematopoietic response to these agents. | Moderate |
| Penicillins, Cephalosporins | Potential antagonism of bactericidal activity in some situations. | Moderate |
| Rifampicin | Decreases chloramphenicol serum levels by inducing metabolism. | Moderate |
| Paracetamol (Acetaminophen) | May increase risk of bone marrow suppression and prolong half-life of chloramphenicol. | Moderate |
7. Patient Counselling
- DO complete the full course as prescribed, even if you feel better.
- DO inform all your doctors and dentists you are taking chloramphenicol.
- DO get regular blood tests (CBC) as advised by your doctor during systemic therapy.
- DONT use leftover medication for a new infection.
- DONT share your eye/ear drops with anyone else.
- DONT use systemic chloramphenicol for colds, flu, or viral infections.
8. Toxicology & Storage
Overdose: Nausea, vomiting, acidosis, hypothermia ('Gray' appearance in infants), cardiovascular collapse, bone marrow hypoplasia leading to pancytopenia, confusion, peripheral neuropathy.
Storage: Store at room temperature (15-25°C), protected from light and moisture. Do not freeze. Keep oral and injectable forms out of reach of children. For eye/ear drops: Once opened, most solutions should be discarded after 28 days (check package insert). Do not use if solution is discolored or contains particles.