ATCVet code: QJ01BA90

Florfenicol is a synthetic broad spectrum antibiotic effective against most Gram-positive and Gram-negative bacteria isolated from domestic animals. Florfenicol acts by inhibiting protein synthesis at the ribosomal level and is bacteriostatic. However, in vitro studies of florfenicol demonstrate bactericidal activity against Mannheimia haemolytica, Pasteurella multocida, Actinobacillus pleuropneumoniae and Histophilus somni.

In vitro testing has shown that florfenicol is active against the bacterial pathogens most commonly isolated in respiratory diseases in cattle (including Pasteurella multocida, Mannheimia haemolytica, and Histophilus somni) and in pigs (including Actinobacillus pleuropneumoniae and Pasteurella multicida). Acquired resistance to florfenicol is mediated by efflux pump resistance associated with a floR gene. Such resistance has not yet been identified in the target pathogens except for Pasteurella multocida. Resistance to florfenicol and other antimicrobials has been identified in the food-borne pathogen Salmonella typhimurium and co-resistance to florfenicol and other antimicrobials (e.g. ceftiofur) has been identified in the microrganisms from the family Enterobacteriaceae.

The administration of the product by the subcutaneous route at the recommended dosage of 40 mg/kg maintains bovine efficacious blood levels (i.e. above the MIC90 of the main respiratory pathogens) for 63 hours. Maximum serum concentration (Cmax) of approximately 5µg/ml, occurs at approximately 5.3 hours (Tmax) after dosing. The mean serum concentration 24 hours after dosing is 2 µg/ml.

Intramuscular administration at the recommended dose of 20 mg/kg maintains efficacious blood levels in cattle for 48 hours. Maximum mean serum concentration (Cmax) of 3.37 µg/ml occurs at 3.3 hours (Tmax) after dosing. The mean serum concentration 24 hours after dosing is 0.77 µg/ml.

The harmonic mean elimination half life was 18.3 hours.

In pigs intravenously administered florfenicol has a mean plasma clearance rate of 5.2 ml/min/kg and a mean volume of distribution at equilibrium of 948 ml/kg. The mean terminal half-life is 2.2 hours.

After initial intramuscular administration of florfenicol, maximum mean serum concentrations of between 3.8 and 13.6 µg/ml are reached after 1.4 hours and the concentrations deplete with a terminal mean half-life of 3.6 hours. After a second intramuscular administration, maximum serum concentrations of between 3.7 and 3.8 µg/ml are reached after 1.8 hours. Serum concentrations drop below 1 µg/ml, the MIC90 for the target porcine pathogens, 12 to 24 hours following IM administration. Florfenicol concentrations achieved in lung tissue reflect plasma concentrations, with a lung:plasma concentration ratio of approximately 1.

After administration to pigs by the intramuscular route, florfenicol is rapidly excreted primarily in urine. The florfenicol is rapidly metabolised.