Single dose pharmacokinetic study of florfenicol in Atlantic salmon ( Salmo salar) in seawater at 11°C

The pharmacokinetics of intravenously and orally administered florfenicol were determined in Atlantic salmon ( Salmo salar) weighing 194±40 g (mean±s.d.). The study was performed at 10.8±1.5°C. A dose of 10 mg florfenicol/kg body weight was administered either intravenously or orally to groups of 85 fish each. At seven time points, from 3 h to 120 h after administration, blood was sampled from 10 individual fish in each group. The plasma was assayed for florfenicol using an HPLC method. The pharmacokinetic modelling of the results was performed using the computer program PCNONLIN. Following intravenous administration, the plasma concentration-time data of florfenicol were best described by a two-compartment open model. The volume of distribution at steady state, V d(ss), and the total body clearance, Cl T, were 1.122 l/kg and 0.086 l/h·kg, respectively. The elimination halflife, t 1 2 β , was estimated as 12.2 h. Following oral administration, the plasma concentration-time data of florfenicol were best described by a one-compartment open model with first order absorption and elimination. Peak plasma concentration, C max, was estimated at 4.0 μg/ml and was estimated to occur at 10.3 h ( T max) following dosing. The bioavailability, F, was estimated at 96.5%. Based on the median minimum inhibitory concentrations (MICs) of 0.8 μg/ml reported for Aeromonas salmonicida, Vibrio anguillarum and Vibrio salmonicida, plasma concentrations should remain above the MIC for 36–40 h following a single oral dose of 10 mg florfenicol/kg.