Florfenicol

Antibiotic Amphenicol

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO 20 mg/kg q12h Duration: 5-7 days
Notes: Off-label use; monitor for gastrointestinal upset.
Cat PO 20 mg/kg q12h Duration: 5-7 days
Notes: Off-label use; monitor for gastrointestinal upset.
Horse IV 10-20 mg/kg q24h Duration: 3-5 days
Notes: Off-label use; administer slowly over 30 minutes.
Cattle SC 40 mg/kg single dose Duration: one time
Notes: For BRD; do not inject more than 10 mL per site.
Cattle IM 20 mg/kg q48h Duration: 3 doses
Notes: For foot rot; alternate injection sites.
Pig IM 15 mg/kg q24h Duration: 3 days
Notes: For respiratory disease; use in feed or water as alternative.
Pig PO (feed) 10 mg/kg q24h Duration: 5 days
Notes: Medicated feed; ensure adequate intake.
Sheep/Goat IM 20 mg/kg q24h Duration: 3-5 days
Notes: Off-label use; observe withdrawal times.
Rabbit PO 20 mg/kg q12h Duration: 5-7 days
Notes: Off-label use; may cause GI disturbances.
Chicken/Turkey PO (water) 20 mg/kg q24h Duration: 3-5 days
Notes: Off-label in some countries; ensure fresh water.

Clinical Indications & Species Uses

General Indications
  • Treatment of bacterial infections caused by susceptible Gram-positive and Gram-negative organisms, including Mycoplasma spp.
Dog (Canine)
  • Treatment of bacterial infections caused by susceptible organisms, including respiratory tract infections, urinary tract infections, and skin infections (off-label use).
Cat (Feline)
  • Treatment of bacterial infections caused by susceptible organisms, including respiratory tract infections and skin infections (off-label use).
Horse (Equine)
  • Treatment of respiratory tract infections caused by susceptible organisms (off-label use).
Cattle (Bovine)
  • Treatment of bovine respiratory disease (BRD) associated with Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni.
  • Treatment of foot rot (interdigital necrobacillosis) associated with Fusobacterium necrophorum and Bacteroides melaninogenicus.
  • Treatment of acute bovine interdigital phlegmon.
Small Ruminants (Sheep / Goat)
  • Treatment of respiratory tract infections caused by susceptible organisms (off-label use).
Rabbit & Small Mammals
  • Treatment of bacterial infections caused by susceptible organisms (off-label use).
Avian & Poultry
  • Treatment of chronic respiratory disease (CRD) associated with Mycoplasma gallisepticum and Escherichia coli in chickens and turkeys (off-label in some countries).
Exotic & Other Species
  • Treatment of bacterial infections in exotic animals (off-label use).

Pharmacology & Mechanism of Action

Drug Class: Antibiotic | Pharmacological Group: Amphenicol

Mechanism of Action: Florfenicol is a broad-spectrum bacteriostatic antibiotic that inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit, specifically at the peptidyl transferase center. This binding prevents the transfer of amino acids to the growing peptide chain, thereby halting protein synthesis. Unlike chloramphenicol, florfenicol is not associated with aplastic anemia in humans and is effective against many chloramphenicol-resistant bacteria due to its resistance to chloramphenicol acetyltransferase.

Pharmacodynamics: Florfenicol exhibits time-dependent bactericidal activity against susceptible organisms, although it is primarily bacteriostatic. It is active against a wide range of Gram-positive and Gram-negative bacteria, including Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, Actinobacillus pleuropneumoniae, Escherichia coli, Salmonella spp., and Mycoplasma spp. Its efficacy is influenced by the concentration at the site of infection and the duration of exposure. Florfenicol also has immunomodulatory effects, such as suppression of inflammatory cytokine production, which may contribute to its clinical efficacy.

⚡ Pharmacokinetics Summary

Absorption: Florfenicol is well absorbed after oral administration in most species, with bioavailability ranging from 75% to 90% in pigs and cattle. In ruminants, oral absorption is slower and less complete due to ruminal degradation, but it is still effective. After intramuscular or subcutaneous injection, absorption is rapid and complete, with peak plasma concentrations achieved within 1-2 hours.
Distribution: Florfenicol is widely distributed throughout the body, achieving therapeutic concentrations in most tissues and fluids, including the lungs, pleural fluid, synovial fluid, and cerebrospinal fluid. It crosses the blood-brain barrier to some extent. The volume of distribution is approximately 0.8-1.0 L/kg in cattle and pigs. It is moderately bound to plasma proteins, with binding ranging from 13% to 19% in cattle and pigs.
Metabolism: Florfenicol is metabolized primarily in the liver, but the extent of metabolism varies by species. In cattle, the major metabolite is florfenicol amine, which is formed by the loss of the fluorine atom. In pigs, metabolism is less extensive, with a significant portion excreted unchanged. The metabolic pathways involve dehalogenation and glucuronidation.
Excretion: Florfenicol and its metabolites are excreted primarily in the urine, with a smaller amount in feces. In cattle, approximately 50-65% of the dose is excreted in urine, and 30-40% in feces. In pigs, urinary excretion accounts for about 70% of the dose. Biliary excretion also occurs but is minor.
Half-Life: Cattle: 2.5-3.5 hours (IV), 3-4 hours (IM); Pigs: 15-20 hours (IM); Dogs: 4-6 hours (oral); Cats: 4-6 hours (oral); Horses: 2-3 hours (IV); Poultry: 5-10 hours (oral)
Bioavailability: Oral: 75-90% in pigs, 50-80% in cattle; IM/SC: nearly 100%
Protein Binding: 13-19% in cattle and pigs; approximately 20% in dogs and cats

Available Formulations & Strengths

Injectable Solution 300 mg/mL (IM, SC)
Oral Powder 2.2% (22 mg/g) (PO)
Oral Solution 100 mg/mL (PO)
Feed Premix Various (e.g., 10%, 20%) (PO)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to florfenicol or other amphenicols.
  • Use in animals with known history of chloramphenicol-induced aplastic anemia (though florfenicol is safer, caution is advised).
  • Concurrent use with bacteriostatic antibiotics that act on the same ribosomal site (e.g., chloramphenicol, thiamphenicol).
  • Use in lactating dairy cattle (if not approved for milk production).
  • Use in animals with severe hepatic or renal impairment (dose adjustment may be needed).
Warnings & Clinical Precautions:
  • Not for use in humans; avoid direct contact with skin and eyes.
  • In cattle, subcutaneous injection may cause local tissue reaction and inflammation; administer in the neck to minimize carcass damage.
  • In pigs, intramuscular injection may cause transient swelling and pain at the injection site.
  • Use with caution in animals with pre-existing hearing or balance disorders, as amphenicols can cause ototoxicity.
  • Prolonged use may result in superinfection with non-susceptible organisms.
  • In food animals, observe withdrawal times to avoid violative residues.
  • Safety in pregnant or lactating animals has not been fully established; use only when clearly needed.
  • In horses, intravenous administration should be slow to avoid adverse reactions.

Adverse Effects & Reactions

Common:

  • Injection site swelling and pain
  • Decreased feed and water consumption
  • Soft stools or diarrhea
  • Transient lethargy

Serious / Severe:

  • Anaphylaxis (rare)
  • Bone marrow suppression (rare, reversible)
  • Ototoxicity (rare)
  • Hepatotoxicity (rare)

Rare:

  • Allergic skin reactions
  • Hemolytic anemia
  • Thrombocytopenia
  • Neurological signs (ataxia, seizures) at high doses

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Chloramphenicol Competitive antagonism; both bind to the 50S ribosomal subunit, reducing efficacy. High
Macrolides (e.g., erythromycin, tylosin) Potential antagonism due to similar mechanism of action; avoid concurrent use. Moderate
Tetracyclines May have additive bacteriostatic effects, but potential for antagonism if used concurrently; monitor. Mild
Beta-lactams (e.g., penicillin, amoxicillin) Potential antagonism because florfenicol is bacteriostatic and beta-lactams require active cell division; avoid concurrent use. Moderate
Aminoglycosides (e.g., gentamicin) Potential additive nephrotoxicity and ototoxicity; monitor renal function. Moderate

Overdose & Toxicity Management

Signs of Toxicity:

  • Depression
  • Anorexia
  • Diarrhea
  • Ataxia
  • Recumbency
  • Respiratory distress
  • Seizures (at very high doses)

Emergency Treatment Protocol: There is no specific antidote. Treatment is symptomatic and supportive. Induce vomiting if recent oral ingestion in dogs and cats. Administer activated charcoal to reduce absorption. Provide intravenous fluids to maintain hydration and electrolyte balance. Monitor for signs of bone marrow suppression and hepatic or renal toxicity. In severe cases, consider blood transfusion if anemia develops.

Food Animal Withdrawal Times

🥩 Meat: 28 days🥛 Milk: 0 days

For cattle: meat withdrawal is 28 days; milk withdrawal is 0 days if used according to label (but extra-label use may require extended withdrawal). For pigs: meat withdrawal is 14 days. For poultry: meat withdrawal is 14 days; eggs withdrawal is not established. Always follow local regulations and veterinary guidance.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 20-25°C (68-77°F), excursions permitted between 15-30°C (59-86°F).

Handling & Special Conditions: Protect from freezing. Keep container tightly closed. Store in a dry place. Avoid exposure to excessive heat.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved for use in cattle (injectable) and swine (injectable and oral) in the US. Not approved for use in dogs, cats, horses, or poultry in the US, but may be used extra-label.

Extra-Label (Off-Label) Use: In the US, florfenicol is approved for use in cattle and swine. Extra-label use in other species or at different doses is permitted under AMDUCA (Animal Medicinal Drug Use Clarification Act) only with a valid veterinary-client-patient relationship and must comply with withdrawal time requirements. In the EU, similar regulations apply under Regulation (EC) No 470/2009.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Florfenicol is a valuable antibiotic for the treatment of respiratory diseases in cattle and pigs, particularly those caused by Mannheimia haemolytica, Pasteurella multocida, and Actinobacillus pleuropneumoniae. It is also effective against foot rot in cattle. Due to its broad-spectrum activity and good tissue penetration, it is often used as a first-line treatment for BRD. In small animals, it is used off-label for infections resistant to other antibiotics. It is important to use florfenicol judiciously to minimize the development of antimicrobial resistance. When administering, ensure proper injection technique to reduce tissue damage. Monitor animals for adverse effects, especially during prolonged therapy. Always adhere to withdrawal times in food animals to ensure food safety.

References & Literature

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