Chloramphenicol

Antibiotic Amphenicol antibiotic

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO 25-50 mg/kg q8h Duration: 5-14 days depending on infection
Notes: Use with caution; monitor for bone marrow suppression.
Cat PO 25-50 mg/kg q12h Duration: 5-14 days
Notes: Cats have slower metabolism; adjust frequency.
Horse IV 25-50 mg/kg q6h Duration: 5-10 days
Notes: Use only if no alternative; risk of human exposure.
Rabbit PO 50 mg/kg q12h Duration: 5-10 days
Notes: Monitor for GI disturbances.
Bird (exotic) PO 50-100 mg/kg q8-12h Duration: 5-10 days
Notes: Use with caution; may cause immunosuppression.

Clinical Indications & Species Uses

General Indications
  • Broad-spectrum antibiotic for susceptible bacterial infections, especially when tissue penetration is needed (CNS, eye, prostate).
Dog (Canine)
  • Treatment of bacterial infections caused by susceptible organisms, including meningitis, brain abscesses, ocular infections, and rickettsial diseases (e.g., ehrlichiosis, Rocky Mountain spotted fever).
Cat (Feline)
  • Treatment of bacterial infections, including meningitis, ocular infections, and rickettsial diseases.
Horse (Equine)
  • Treatment of bacterial infections, particularly meningitis, pneumonia, and septicemia, when other antibiotics are ineffective.
Rabbit & Small Mammals
  • Treatment of bacterial infections, particularly those involving the CNS or eyes.
Exotic & Other Species
  • Treatment of bacterial infections in reptiles, small mammals, and exotic pets, especially for CNS or ocular infections.

Pharmacology & Mechanism of Action

Drug Class: Antibiotic | Pharmacological Group: Amphenicol antibiotic

Mechanism of Action: Chloramphenicol inhibits bacterial protein synthesis by binding reversibly to the 50S ribosomal subunit, specifically to the peptidyl transferase center, preventing peptide bond formation. It is primarily bacteriostatic but can be bactericidal at high concentrations against some organisms. It has a broad spectrum of activity against many Gram-positive and Gram-negative bacteria, as well as rickettsiae, chlamydiae, and mycoplasmas.

Pharmacodynamics: Chloramphenicol exhibits time-dependent killing with a post-antibiotic effect. Its activity is best correlated with the duration of time that serum concentrations exceed the minimum inhibitory concentration (MIC). It is effective against anaerobic organisms and penetrates well into tissues, including the CNS, eye, and prostate. Resistance can occur via plasmid-encoded chloramphenicol acetyltransferase, which inactivates the drug.

⚡ Pharmacokinetics Summary

Absorption: Chloramphenicol is well absorbed after oral administration in most species, but absorption may be erratic in ruminants due to ruminal degradation. The palmitate ester is hydrolyzed in the small intestine to release active chloramphenicol. Injectable forms are well absorbed after IM or SC administration.
Distribution: Chloramphenicol is widely distributed throughout the body, including the brain, cerebrospinal fluid, aqueous humor, and synovial fluid. It crosses the placenta and is distributed into milk. It has a volume of distribution of approximately 1-2 L/kg in dogs and cats.
Metabolism: Chloramphenicol is primarily metabolized in the liver by glucuronidation to inactive metabolites. In dogs, the half-life is relatively short (about 1-2 hours), while in cats it is longer (about 5 hours) due to slower glucuronidation. In horses, the half-life is approximately 1-2 hours.
Excretion: Metabolites and unchanged drug are excreted primarily in the urine, with some biliary excretion. In neonates, renal excretion is reduced, leading to prolonged half-life.
Half-Life: Dog: 1-2 hours; Cat: 5 hours; Horse: 1-2 hours; Cattle: 2-4 hours (but oral bioavailability is poor); Rabbit: 1-2 hours
Bioavailability: Oral: 70-90% in dogs and cats; in ruminants, oral bioavailability is low due to ruminal degradation. IM: variable, but generally good.
Protein Binding: Approximately 30-50% bound to plasma proteins in most species.

Available Formulations & Strengths

Oral Tablet 100 mg, 250 mg, 500 mg (PO)
Oral Capsule 250 mg, 500 mg (PO)
Oral Suspension (palmitate) 25 mg/mL, 50 mg/mL (PO)
Injectable Solution 100 mg/mL, 250 mg/mL (IV, IM, SC)
Ophthalmic Ointment 1% (Ophthalmic)
Otic Solution 0.5% (Otic)

Contraindications & Clinical Warnings

Contraindications:
  • Known hypersensitivity to chloramphenicol
  • Use in animals with bone marrow depression or blood dyscrasias
  • Use in pregnant animals (risk of fetal toxicity)
  • Use in neonates (especially in cats and dogs) due to risk of 'gray baby syndrome'
  • Concurrent use with drugs that cause bone marrow suppression
Warnings & Clinical Precautions:
  • Chloramphenicol is a human carcinogen and can cause aplastic anemia in humans; handle with extreme care, wear gloves, and avoid skin contact.
  • Use with caution in animals with hepatic or renal impairment.
  • Prolonged use may result in superinfection with resistant organisms.
  • In food animals, extra-label use is prohibited in the US (see regulatory notes).
  • May cause immunosuppression; use with caution in immunocompromised animals.

Adverse Effects & Reactions

Common:

  • Anorexia
  • Vomiting
  • Diarrhea
  • Reversible bone marrow suppression (dose-dependent)

Serious / Severe:

  • Aplastic anemia (idiosyncratic, rare in animals but possible)
  • Gray baby syndrome in neonates (cardiovascular collapse)
  • Peripheral neuropathy (with prolonged use)

Rare:

  • Hypersensitivity reactions
  • Hepatotoxicity
  • Optic neuritis

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Phenobarbital Chloramphenicol may inhibit hepatic metabolism of phenobarbital, increasing its serum levels and toxicity. High
Warfarin and other anticoagulants Chloramphenicol may enhance the anticoagulant effect by inhibiting hepatic metabolism. High
Iron supplements Chloramphenicol may interfere with hematinic response to iron, especially in anemia treatment. Moderate
Macrolides and lincosamides Potential antagonism due to competition for binding site on the 50S ribosomal subunit. Moderate
Cyclophosphamide Chloramphenicol may reduce the activation of cyclophosphamide, decreasing its efficacy. Moderate

Overdose & Toxicity Management

Signs of Toxicity:

  • Vomiting
  • Diarrhea
  • Anorexia
  • Bone marrow suppression
  • Cardiovascular collapse (in neonates)
  • Metabolic acidosis

Emergency Treatment Protocol: There is no specific antidote. Treatment is symptomatic and supportive. Induce vomiting if recent ingestion and animal is conscious. Administer activated charcoal to reduce absorption. Provide IV fluids and supportive care. Monitor blood counts and organ function. In severe cases, blood transfusion may be necessary.

Food Animal Withdrawal Times

Chloramphenicol is prohibited for use in food-producing animals in the United States and many other countries due to the risk of aplastic anemia in humans. Therefore, no withdrawal times are established. Use in food animals is illegal.

Storage, Handling & Regulatory Information

Storage Temperature: Store at room temperature (15-30°C) in a tight, light-resistant container.

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Protect from moisture and light. Do not freeze oral suspensions.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved for use in dogs and cats (oral and injectable forms) but not for food animals. Some formulations may be approved for other species.

Extra-Label (Off-Label) Use: In the US, chloramphenicol is prohibited for extra-label use in food-producing animals under AMDUCA. It is not approved for use in any food animal species. Use in companion animals is allowed with a prescription.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Chloramphenicol is a broad-spectrum antibiotic with excellent tissue penetration, particularly into the CNS and eye. It is a valuable option for treating meningitis, brain abscesses, and ocular infections when other antibiotics are ineffective or contraindicated. However, its use is limited by the potential for serious adverse effects, including bone marrow suppression and the risk of aplastic anemia in humans handling the drug. It should be reserved for cases where no safer alternative exists. In cats, dosing interval should be extended due to slower metabolism. In neonates, avoid use due to the risk of gray baby syndrome. Always wear gloves when handling chloramphenicol and wash hands thoroughly after administration. Monitor complete blood counts during prolonged therapy.

References & Literature

  • 📚 Plumb's Veterinary Drug Handbook
  • 📚 Papich Veterinary Pharmacology and Therapeutics
  • 📚 Compendium of Veterinary Products (CVP)