Chemistry/Storage/Stability/Compatibility - A fluorinated analog of thiamphenicol, florfenicol is commercially available as light yellow to straw-colored injectable solution also containing n-ethyl-2-pyrolidone, propylene glycol and polyethylene glycol. It should be stored between 2°-30°C (36°-86°F).
Pharmacology - Like chloramphenicol, florfenicol is a broad spectrum antibiotic that has activity against many bacteria. It acts by binding to the 50S ribosome, thereby inhibiting bacterial protein synthesis.
Uses/Indications - The drug is approved for use in cattle only (in the USA) for the treatment of bovine respiratory disease (BRD) associated with Pasteurella haemolytica, Pasteurella multocida and Haemophilus somnus.
Because florfenicol has activity against a wide range of microorganisms (e.g., Mycoplasma), it may be useful for treating other infections in cattle (or other species) as well, but specific data supporting these uses is presently lacking.
Pharmacokinetics - After IM injection, approximately 79% of the dose is bioavailable. The drug appears to be well distributed throughout the body, including achievement of therapeutic levels in the CSF. In cattle, only about 13% is bound to serum proteins. Mean serum half life is 18 hours, but wide interpatient variation exists.
Contraindications/Precautions/Reproductive Safety - No contraindications are listed in the package insert, but see residue warnings (below). Safety or effects when used in breeding cattle, during pregnancy or during lactation are unknown and the manufacturer states that the drug is not for use in cattle of breeding age. Caution: Do not give this drug IV.
Adverse Effects/Warnings - Noted transient adverse reactions in cattle include anorexia, decreased water consumption or diarrhea. Injection site reactions can occur that may result in trim loss. Reactions may be more severe if injected at sites other than the neck.
Overdosage - In toxicology studies where feeder calves were injected with up to 10X of the recommended dosage, the adverse effects noted above were seen, plus increased serum enzymes were noted. These effects were generally transient in nature. Long term (43 day) standard dosage studies showed a transient decrease in feed consumption, but no long-term negative effects were noted.
Drug Interactions - No specific drug interactions for florfenicol were located, but the drug may behave similarly to chloramphenicol. If so, florfenicol could antagonize the bactericidal activity of the penicillins or aminoglycosides. This antagonism has not been demonstrated in vivo, and these drug combinations have been used successfully many times clinically. Other antibiotics that bind to the 50S ribosomal subunit of susceptible bacteria (erythromycin, clindamycin, lincomycin, tylosin, etc.) may potentially antagonize the activity of chloramphenicol or vice versa, but the clinical significance of this potential interaction has not been determined. For other drug interactions that florfenicol may share with chloramphenicol, see that monograph or refer to other drug information resources.
For treatment of BRD:
a) 20 mg/kg IM (in neck muscle only); repeat in 48 hours. Alternatively, a single 40 mg/kg SubQ dose (in neck) may be used. Note: 20 mg/kg equates to 3 ml of the injection per 100 lb. of body weight. Do not exceed 10 ml per injection site. (Nuflor® Package Insert—Schering Plough)
Monitoring Parameters -1) Clinical efficacy 2) Injection site reactions
Client Information - Residue Warnings: Slaughter withdrawal is 28 days post injection if using the IM route; 38 days after the SubQ route. Not to be used in female dairy cattle 20 months of age or older. A withdrawal period has not been established in preruminating calves. Do not use in calves to be processed for veal.
Dosage Forms/Preparations/FDA Approval Status -
Florfenicol Injection 300 mg/ml in 100 ml, 250 ml and 500 ml multi-dose vials; NuFlor® (Schering-Plough); (Rx). Approved for use in cattle; see residue warnings above.
Human-Approved Products: None
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