Florfenicol
Fluorinated analog of thiamphenicol (Sch-25298)
Also known as: Nuflor Gold · Resflor Gold · Aquaflor · Osurnia · Sch-25298 · Florfenicolum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible systemic (bacterial or rickettsial) infections | 20 mg/kg | IM | q8h | 3-5 days | 🌎 NA |
| Otitis externa (associated with Staphylococcus pseudintermedius and Malassezia pachydermatis) | 1 tube (1.2 g) per infected ear | topical | Repeat once after 7 days | 2 doses total | 🌍 EU |
- Susceptible systemic (bacterial or rickettsial) infections: Used when myelotoxic potential of chloramphenicol is to be avoided.
- Otitis externa (associated with Staphylococcus pseudintermedius and Malassezia pachydermatis): Clean ear before first dose. Do not clean before second dose or for 14 days after.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible systemic (bacterial or rickettsial) infections | 22 mg/kg | IM, PO | q12h | 3-5 days | 🌎 NA |
- Susceptible systemic (bacterial or rickettsial) infections: Oral dosage form not available, but solution given orally to experimental cats was well absorbed.
Cattle
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Bovine respiratory disease (BRD) | 20 mg/kg | IM | repeat in 48 hours | 2 doses | 🌎 NA |
| Bovine respiratory disease (BRD) | 40 mg/kg | SC | once | Single dose | 🌎 NA |
| Bovine respiratory disease (BRD) | 40 mg/kg (6 mL/100 lb B.W .) | SC | once | Single dose | 🌎 NA |
| BRD and control of BRD-associated pyrexia | 40 mg/kg florfenicol/2.2 mg/kg flunixin (6 mL/100 lb. B.W .) | SC | once | Single dose | 🌎 NA |
- Bovine respiratory disease (BRD): In neck muscle only. Do not exceed 10 mL per injection site.
- Bovine respiratory disease (BRD): In neck only.
- Bovine respiratory disease (BRD): Do not administer more than 15 mL at each site. Neck only.
- BRD and control of BRD-associated pyrexia: Do not administer more than 10 mL at each site. Neck only.
Swine
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Swine respiratory disease | In water at a concentration of 400 mg/gallon (100 ppm) | PO | continuous | 5 days | 🌎 NA |
- Swine respiratory disease: Use as only source of drinking water.
Sheep
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Respiratory disease complex in kids | 20 mg/kg a day | IM | q24h | 2 days | 🌎 NA |
- Respiratory disease complex in kids: Route not specified; assume IM.
Goats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Respiratory disease complex in kids | 20 mg/kg a day | IM | q24h | 2 days | 🌎 NA |
- Respiratory disease complex in kids: Route not specified; assume IM.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Florfenicol is a synthetic, broad-spectrum, bacteriostatic antibiotic structurally related to chloramphenicol and thiamphenicol.
Key Clinical Features:
- Safety Profile: Unlike chloramphenicol, florfenicol lacks the p-nitro group associated with idiosyncratic, irreversible aplastic anemia in humans. This makes it significantly safer for use in food-producing animals and for the humans handling the medication.
- Veterinary Approvals: FDA-approved primarily for use in cattle (Bovine Respiratory Disease), swine, and aquaculture (fish).
- Off-label Use: Frequently utilized off-label in small animals (dogs and cats) and exotic species for susceptible systemic bacterial or rickettsial infections, particularly when the myelotoxic potential of chloramphenicol must be avoided.
- Spectrum of Activity: Highly effective against Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma bovis, as well as a wide range of other Gram-positive and Gram-negative organisms.
Mechanism of action
Florfenicol is a time-dependent, primarily bacteriostatic antibiotic (though it can be bactericidal against certain highly susceptible respiratory pathogens).
- Mechanism: It readily penetrates bacterial cells and binds reversibly to the 50S ribosomal subunit.
- Pathway: Binding to the 50S subunit → inhibits the enzyme peptidyl transferase → prevents peptide bond formation → inhibits bacterial protein synthesis.
- Resistance: Because it is fluorinated at the 3' position, it is resistant to inactivation by chloramphenicol acetyltransferase, an enzyme that confers resistance to chloramphenicol in many bacteria.
Safety & warnings
Contraindications
- Intravenous (IV) administration
- Veal calves or preruminating calves
- Cattle or swine of breeding age (effects on reproduction unknown)
- Female dairy cattle 20 months of age or older
- Tympanic membrane rupture (perforated eardrum)
- Hypersensitivity to florfenicol, terbinafine, or betamethasone
- Dogs with generalized demodicosis (due to corticosteroid component)
Adverse effects
- Cattle: Anorexia, decreased water consumption, diarrhea
- Cattle: Injection site reactions (may result in trim loss)
- Cattle: Anaphylaxis and collapse (rare)
- Small Animals: Pain on IM injection
- Small Animals: Gastrointestinal effects, including severe diarrhea
- Mild application site erythema
- Head shaking
- Transient hearing loss (rare)
- Altered hearing or deafness in older dogs (rare)
Precautions
Important Administration Warning: Do NOT administer intravenously (IV).
- Injection Site: In cattle, injections should be given only in the neck muscle to minimize trim loss and severe tissue reactions.
- Volume Limits: Do not exceed 10 mL (or 15 mL for Nuflor Gold) per injection site in cattle.
- Residue Warnings: Strict adherence to slaughter withdrawal times is legally required for food-producing animals. Do not use in female dairy cattle ≥20 months of age or in veal calves.
- Reproductive Safety: Safety in breeding, pregnant, or lactating animals has not been established.
Drug interactions
May antagonize the bactericidal activity of penicillins (theoretical, though often used together clinically).
May antagonize the bactericidal activity of aminoglycosides.
May potentially antagonize activity due to competition for binding at the 50S ribosomal subunit.
May potentially antagonize activity due to competition for binding at the 50S ribosomal subunit.
Monitoring
- Clinical efficacy (resolution of infection/fever)
- Injection site reactions (swelling, pain, tissue necrosis)
- Gastrointestinal signs (appetite, stool consistency)
- Resolution of clinical signs of otitis externa
- Cytology to confirm clearance of bacteria and yeast
- Integrity of the tympanic membrane
Pharmacokinetics
Half-life
Absorption
Cattle: ~79% bioavailable after IM injection. Dogs: Poorly absorbed after SC injection; good bioavailability (95%) after PO administration. Cats: High absorption of a 100 mg/mL solution when given IM or PO.
Distribution
Well distributed throughout the body, achieving therapeutic levels in the CSF. Cattle: Volume of distribution is ~0.7 L/kg; ~13% bound to serum proteins.
Metabolism
Primarily hepatic metabolism (inferred from amphenicol class).
Elimination
Dogs: Total body clearance is ~1 L/kg/hr after IV administration; eliminated rapidly after PO administration.
Overdose
In toxicology studies, feeder calves injected with up to 10X the recommended dosage exhibited transient adverse effects (anorexia, decreased water consumption, diarrhea) and increased serum enzymes. Long-term (43 day) standard dosage studies showed a transient decrease in feed consumption, but no long-term negative effects were noted. Treatment of acute overdose should be supportive and symptomatic.
Available products
Formulations
- Injectable solution
- Concentrate solution (water additive)
- Feed additive
- Topical ear gel (10 mg florfenicol, 10 mg terbinafine, 1 mg betamethasone acetate per 1.2 g dose)
Veterinary
- Florfenicol Injection: 300 mg/mL (NuFlor, Nuflor Gold)
- Florfenicol 2.3% (23 mg/mL) Concentrate Solution (NuFlor Concentrate Solution)
- Florfenicol 300 mg/mL with Flunixin 16.5 mg/mL Injection (Resflor Gold)
- Florfenicol feed additives (Aquaflor for fish, and swine feed formulations)
- Osurnia ear gel (10 mg florfenicol, 10 mg terbinafine, 1 mg betamethasone acetate per tube)
Regulatory status
POM-V
POM-V
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Florfenicol injection (Nuflor, Nuflor Gold) should be stored between 2°-30°C (36°-86°F). Use within 28 days of first use. The oral solution (swine) should be stored between 2°-26°C (36°-77°F). Resflor Gold should not be stored above 30°C (86°F), used within 28 days, and the vial should not be punctured more than 10 times.
Client information
For Small Animal Owners (Dogs & Cats)
- Administration: If giving this medication orally (using the liquid formulation off-label), it may taste bitter. Ensure your pet swallows the full dose.
- Side Effects: Watch for gastrointestinal upset, particularly severe diarrhea or loss of appetite. Contact your veterinarian if these occur.
- Injections: If your pet is receiving injections at the clinic, the injection site may be temporarily painful or sore.
For Livestock Owners (Cattle & Swine)
- Strict Withdrawal Times:
- Cattle: 28 days post-injection for IM route; 38 days for SC route (44 days for Nuflor Gold).
- Swine: 16 days (in drinking water).
- Restrictions: Do NOT use in female dairy cattle 20 months of age or older. Do NOT use in calves to be processed for veal.
- Injection Technique: Administer injections only in the neck muscle to prevent carcass trim loss. Do not exceed the recommended volume per injection site.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.