Pharmacotherapeutic group: Antibacterials for systemic use, amphenicols
ATC Vet Code: QJ01BA90
Pharmacodynamic properties
Florfenicol, a broad-spectrum synthetic antibiotic belonging to the phenicol group, acts by inhibiting protein synthesis at the ribosomal level, resulting in a bacteriostatic effect. In vitro studies have shown that florfenicol is active against the bacterial pathogens most commonly isolated in respiratory diseases in pigs, including Actinobacillus pleuropneumoniae and Pasteurella multocida. Furthermore, florfenicol exhibits bactericidal activity in vitro, particularly when maintained at concentrations exceeding the Minimal Inhibitory Concentration (MIC), for a duration of up to 12 hours.
Resistance to florfenicol is found in the floR gene, strongly associated with the floR efflux pump, which is usually plasmid-mediated and transferred horizontally into other Pasteurellaceae species. At least the following plasmids have been found to be the carrier of the floR genes on Pasteurellaceae species: pFA11, pMAF5, pMAF6, pM3446F, p518, pCCK381, pCCK1900.
Resistance to florfenicol has also been detected in Salmonella typhimurium and other foodborne pathogens.
There is cross-resistance between substances of the phenicol class. Additionally, other resistance genes have been identified that can be located on plasmids or transposons, such as the cfr gene, which confers cross-resistance between pleuromutilins, oxazolidinones, phenicols, streptogramin A, and lincosamides.
Pharmacokinetic particulars
After administration to pigs by gavage at 15 mg/kg under experimental conditions, absorption of florfenicol was variable but peak serum concentrations of approximately 5 μg/mL were reached approximately 2 hours after dosing. The terminal half-life was between 2 and 3 hours. When pigs were given free access, for 5 days, to water medicated with florfenicol at a concentration of 100 mg florfenicol per litre of water, serum concentrations of florfenicol exceeded 1 μg/mL for the entire 5 day treatment period except for a couple of short excursions below 1 μg/mL.
After absorption and distribution, florfenicol is extensively metabolised by pigs and rapidly eliminated, primarily in urine.
After parenteral dosing of florfenicol to pigs, it has been shown that lung concentrations are similar to serum concentrations.
Environmental properties
Florfenicol is toxic for cyanobacteria, groundwater organisms, and terrestrial plants.