Pharmacokinetics of Florfenicol and Its Metabolite Florfenicol Amine in Atlantic Salmon

The plasma pharmacokinetic profile of the antibacterial agent florfenicol was studied in Atlantic salmon Salmo salar in seawater. In a single-dose study, each fish was given 10 mg/kg body weight by intravenous (iv) injection or by oral gavage of feed coated with the drug. In a multidose study, pelleted feed coated with 2 g florfenicol/kg was hand-fed daily for 10 d at a dosage of 10 mg florfenicol/kg body weight. The pellets contained small, X-ray-dense glass beads (hallotini). The feed intake was assessed by counting the number of ballotini on X-ray pictures of sampled fish. In a depletion study, the concentration of the marker residue, florfenicol amine, was determined in muscle and liver after a field trial in which the fish were medicated with feed coated with florfenicol for 10 d at a dosage of 10 mg/kg body weight. In the single-dose study, the iv data were best described by a two-compartment open model; the elimination half time. t1/2β, was estimated at 14.7 h. The maximum plasma concentration was 9.l μg/mL, observed at 6 h. The bioavailability was 99%. The maximum plasma concentration observed in the multidose study and the maximum concentration predicted from the single-dose study corresponded very well, which demonstrated the value of single-dose studies. In the depletion study, the upper 95% confidence band for individual observations intercepted the limit of detection for the analytical method after 21 d in muscle and after 27 d in the liver.