Chloramphenicol

BRAND NAMES

• Chloromycetin – the classic, widely recognized brand. 
• Chlorsig – used in many countries, especially Australia and Europe. 
• Ledercide – often used for topical formulations. 
• Opticlor – specifically for eye drops. 
• Capol – another brand in some regions.

MECHANISM OF ACTION

Chloramphenicol is a broad-spectrum antibiotic that works by binding to the 50S subunit of bacterial ribosomes, inhibiting the enzyme peptidyl transferase and preventing protein synthesis. This stops bacterial growth, making it bacteriostatic. It is effective against many Gram-positive, Gram-negative, and anaerobic bacteria.

PHARMACOKINETICS

Absorption

Chloramphenicol is well absorbed orally, with 70–90% bioavailability, reaching peak blood levels within 1–2 hours. Intravenous administration provides complete absorption, while topical forms like eye drops are absorbed mainly at the site of application with minimal systemic exposure.

Distribution

Chloramphenicol is widely distributed throughout the body, including lungs, liver, kidneys, cerebrospinal fluid (CSF), and aqueous humor of the eye. It has a volume of distribution (Vd) of approximately 0.6–1 L/kg in adults. The drug crosses the blood-brain barrier, especially when the meninges are inflamed, making it useful for bacterial meningitis.

Metabolism

Chloramphenicol is primarily metabolized in the liverby glucuronidation, forming inactive chloramphenicol glucuronide, which is then excreted in the urine. In newborns and patients with liver impairment, metabolism is slower, increasing the risk of toxicity.

Excretion

Chloramphenicol is primarily excreted by the kidneys as inactive glucuronide. About 10% of the drug is excreted unchanged in urine. The elimination half-life is approximately 1.5–4 hours in healthy adults but may be longer in newborns or patients with liver/kidney impairment.

PHARMACODYNAMICS

It is broad-spectrum and can penetrate tissues, including the CSF, making it effective against serious infections like meningitis.

ADMINISTRATION

Chloramphenicol is given orally, intravenously, or as eye/ear drops depending on the infection. It must be used under medical supervision with correct dosage, as it can cause serious side effects.

DOSAGE AND STRENGTH

 Oral/IV (systemic infections): 50–100 mg/kg/day divided every 6 hours in children; 1–4 g/day divided every 6 hours in adults, depending on infection severity.

• Topical (eye infections): 1–2 drops in the affected eye every 2–6 hours; ointment applied 3–4 times daily.
• Duration: Typically 7–14 days for systemic infections, or as directed based on clinical response.
• Notes: Dose adjustment may be required in liver or kidney impairment; systemic use requires monitoring for bone marrow suppression.

DRUG INTERACTIONS

• Warfarin – Chloramphenicol may increase anticoagulant effects, raising bleeding risk.

• Phenytoin and Sulfonylureas – Can increase plasma levels, leading to toxicity.

• CYP450-metabolized drugs – Chloramphenicol inhibits CYP450 enzymes, affecting drugs like theophylline, chlorpropamide, or tolbutamide.

• Bone marrow suppressants – Concurrent use may increase risk of aplastic anemia.

• Other antibiotics – May have additive or antagonistic effects depending on the combination.

FOOD INTERACTIONS

Chloramphenicol absorption can be slightly affected by food, but there are no major food restrictions. Taking it with meals may reduce stomach upset without significantly affecting effectiveness. Patients should avoid alcohol, as it can increase liver stress during systemic therapy.

CONTRAINDICATIONS

Chloramphenicol should not be used in patients with known hypersensitivity to the drug, a history of blood disorders such as aplastic anemia, or severe liver disease. It is also contraindicated in newborns and premature infants due to the risk of gray baby syndrome, and in patients with porphyria, as it may trigger or worsen symptoms.

SIDE EFFECTS

• Nausea, vomiting, diarrhea 
• Bone marrow suppression, anemia, leukopenia, thrombocytopenia 
• Rash, fever, hypersensitivity 
• Headache, dizziness 
• Gray baby syndrome in infants 

OVER DOSE

• Nausea, vomiting, diarrhea 
• Bone marrow suppression, anemia, leukopenia, thrombocytopenia 
• Rash, fever, hypersensitivity 
• Headache, dizziness 
• Gray baby syndrome in infants 

TOXICITY

Chloramphenicol toxicity can cause bone marrow suppression, including reversible anemia and rare aplastic anemia. In neonates, it may lead to gray baby syndrome, and prolonged use can rarely cause peripheral neuropathy or liver toxicity.