Pharmacoterapeutic group: Antibacterials for systemic use
ATCvet code: QJ01BA90.
Pharmacodynamic properties
Florfenicol is a systemic 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, Histophilus somni and Arcanobacterium pyogenes) and in pigs (including Actinobacillus pleuropneumoniae and Pasteurella multocida).
Pharmacokinetic properties
Cattle:
In cattle, intramuscular administration at the recommended dose of 20 mg/kg maintains efficacious blood levels for 48 hours. Maximum mean serum concentration (Cmax) of 2.55 μg/ml occurs at 4.7 hours (Tmax) after dosing. The mean serum concentration 24 hours after dosing was 1.4 μg/ml. The harmonic mean elimination half life was 26.2 hours.
Pigs:
After initial intramuscular administration of florfenicol, maximum serum concentrations of between 1.9 and 3.1 μg/ml are reached after 2.2 hours and the concentrations deplete with a terminal mean half-life of 35.5 hours. After a second intramuscular administration, maximum serum concentrations of between 2.0 and 8.1 μg/ml are reached after 1.7 hours. Florfenicol concentrations achieved in lung tissue reflect plasma concentrations, with a lung:plasma concentration ratio of approximately 1.
After administration to pigs by intramuscular route, florfenicol is rapidly excreted, primarily in urine. The florfenicol is extensively metabolised.