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Sunday, July 27, 2025

Chloramphenicol


Chloramphenicol is a broad-spectrum antibiotic with potent bacteriostatic activity, used systemically (rarely) and topically (more commonly) for the treatment of serious infections and localized bacterial conditions, particularly of the eye and ear. Initially derived from Streptomyces venezuelae, chloramphenicol is now produced synthetically. Despite its efficacy, systemic use is limited due to the risk of severe side effects such as aplastic anemia and bone marrow suppression.

This professional profile covers chloramphenicol's classification, mechanism of action, spectrum, clinical uses, dosing, contraindications, adverse effects, precautions, and drug interactions.

Pharmacological Classification

  • Therapeutic class: Antibacterial agent

  • Pharmacologic class: Broad-spectrum protein synthesis inhibitor

  • ATC Code: S01AA01 (ophthalmic), J01BA01 (systemic use)

Mechanism of Action

Chloramphenicol binds to the 50S subunit of the bacterial ribosome, specifically at the peptidyl transferase site, inhibiting peptide bond formation. This prevents the elongation of the protein chain during translation, exerting a bacteriostatic effect.

  • At high concentrations, it may be bactericidal against certain strains, especially Haemophilus influenzae, Neisseria meningitidis, and Streptococcus pneumoniae.

  • It does not affect human cytoplasmic ribosomes but may affect mitochondrial ribosomes, contributing to hematologic toxicity.

Antimicrobial Spectrum

Gram-Positive Bacteria

  • Streptococcus pneumoniae

  • Staphylococcus aureus (non-MRSA strains)

  • Listeria monocytogenes

Gram-Negative Bacteria

  • Haemophilus influenzae

  • Neisseria meningitidis, N. gonorrhoeae

  • Escherichia coli, Salmonella spp., Shigella spp.

Anaerobes

  • Bacteroides fragilis, Clostridium spp.

Others

  • Rickettsiae

  • Chlamydia (limited activity)

  • Mycoplasma pneumoniae (moderate activity)

It does not cover Pseudomonas aeruginosa or most resistant gram-negative bacilli.

Clinical Indications

Topical (Ophthalmic or Otic)

  • Bacterial conjunctivitis (first-line for adults and children in UK)

  • Blepharitis, keratitis, corneal ulcers (mild to moderate)

  • Postoperative prophylaxis in eye surgeries

  • Bacterial otitis externa (ear drops with or without corticosteroids)

Systemic (IV or Oral) – rare, reserved for serious infections

  • Typhoid and paratyphoid fever (in areas of resistance to safer antibiotics)

  • Rickettsial infections (e.g., Rocky Mountain spotted fever)

  • Meningitis (in penicillin-allergic patients)

  • Brain abscess (penetrates CNS well)

  • Anaerobic infections, particularly when metronidazole cannot be used

Off-label/Second-line uses

  • Multidrug-resistant Salmonella infections

  • Refractory ocular infections

  • Serious infections in developing countries with limited antibiotic access

Dosage and Administration

Topical Eye Drops (0.5%)

  • Adults and children: 1–2 drops into affected eye every 2–6 hours

  • Once improvement noted, reduce to every 4–6 hours

  • Maximum duration: 5–7 days

Eye Ointment (1%)

  • Applied to conjunctival sac 3–4 times daily, often at night

Otic Solution

  • Instill 2–3 drops into ear canal 2–3 times daily

  • Often used with steroid combinations

Systemic Oral or IV (by specialist only)

  • Adults: 50–100 mg/kg/day in 4 divided doses

  • Children: 25–100 mg/kg/day (depending on severity)

  • Neonates: Reduced dose due to immature liver (risk of Gray Baby Syndrome)

  • Duration depends on indication, typically 7–14 days

Pharmacokinetics (Systemic Use)

  • Absorption: Rapid oral absorption (bioavailability ~80%)

  • Distribution: Widely distributed, including CSF and eye tissues

  • Metabolism: Liver (glucuronidation)

  • Excretion: Urine (~90%)

  • Half-life: 1.5–4 hours in adults; longer in neonates

  • Crosses placenta and is found in breast milk

Contraindications

  • Hypersensitivity to chloramphenicol

  • Previous history of blood dyscrasias or bone marrow suppression

  • Pregnancy and lactation (systemic use) – potential hematologic effects

  • Infants <2 weeks (systemic) – risk of Gray Baby Syndrome

  • Topical use in viral or fungal ocular infections

Warnings and Precautions

  • Systemic Use: Reserved only for severe, life-threatening infections

  • Prolonged or repeated use (especially topical) increases risk of hypersensitivity, superinfection, and hematologic toxicity

  • Monitor CBC during systemic therapy (weekly if >1 week)

  • Avoid prolonged eye drop use beyond 7 days without reassessment

  • Caution in renal or hepatic impairment

Adverse Effects

Topical

  • Transient stinging or burning on application

  • Contact dermatitis

  • Local irritation, redness, itching

  • Rare: Hypersensitivity reactions, anaphylaxis, angioedema

  • Prolonged use: Risk of superinfection or fungal overgrowth

Systemic

  • Bone marrow suppression (dose-related, reversible)

  • Aplastic anemia (rare, idiosyncratic, potentially fatal)

  • Leukopenia, thrombocytopenia

  • Gray Baby Syndrome (neonates): vomiting, cyanosis, hypotension, death

  • GI upset: nausea, vomiting, diarrhea

  • Neurotoxicity (rare): headache, confusion, optic neuritis

Drug Interactions

  • Warfarin: Inhibits metabolism → ↑ INR, ↑ bleeding risk

  • Phenytoin, tolbutamide, chlorpropamide: metabolism inhibition → ↑ drug levels

  • Live vaccines (typhoid): reduced efficacy during chloramphenicol use

  • Other bone marrow depressants (e.g., cancer drugs): additive hematotoxicity

  • Cyclosporine, tacrolimus: Increased risk of nephrotoxicity

Pregnancy and Lactation

Pregnancy

  • Systemic use contraindicated

  • Risk of fetal hematologic toxicity

  • Topical use (eye/ear) may be acceptable under specialist advice

Lactation

  • Excreted in breast milk; avoid systemic use

  • Topical use: caution, minimal systemic absorption, but monitor infant

Use in Special Populations

  • Neonates: Systemic use contraindicated due to immature metabolism

  • Pediatrics: Eye drops widely used and safe when short-term

  • Geriatrics: Caution in systemic use; monitor hematologic status

  • Liver disease: May impair metabolism → increased toxicity risk

Counseling Points

  • Wash hands before and after applying eye or ear drops

  • Do not touch dropper tip to eye or ear surface

  • Finish the full course even if symptoms improve

  • Store eye drops in the refrigerator if instructed; discard after 28 days

  • Report any signs of rash, bruising, or bleeding (if systemic use)

  • Do not use longer than prescribed duration without review

  • Avoid contact lenses during treatment for eye infections

  • Seek urgent care if vision changes, persistent pain, or severe swelling occur

Clinical Notes

  • First-line topical treatment for bacterial conjunctivitis in many guidelines (e.g., UK NHS)

  • Due to its serious risks, systemic use is typically restricted to hospital settings or under specialist care

  • Resistance is uncommon in ophthalmic use but should be considered in treatment failure

  • Topical formulations are preferred due to low systemic absorption and reduced risk of toxicity




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