SINGLE-DOSE PHARMACOKINETIC STUDY OF FLORFENICOL IN ATLANTIC SALMON (SALMO-SALAR) IN SEAWATER AT 11-DEGREES-C

The pharmacokinetics of intravenously and orally administered florfeni col were determined in Atlantic salmon (Salmo salar) weighing 194 +/- 40 g (mean +/- s.d.). The study was performed at 10.8 +/- 1.5-degrees- 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 point s, from 3 h to 120 h after administration, blood was sampled from 10 i ndividual fish in each group. The plasma was assayed for florfenicol u sing an HPLC method. The pharmacokinetic modelling of the results was performed using the computer program PCNONLIN. Following intravenous a dministration, the plasma concentration-time data of florfenicol were best described by a two-compartment open model. The volume of distribu tion at steady state, V(d(ss)), and the total body clearance, CIT, wer e 1. 122 1/kg and 0.086 1/h.kg, respectively. The elimination halflife , t1/2beta, was estimated as 12.2 h. Following oral administration, th e plasma concentration-time data of florfenicol were best described by a one-compartment open model with first order absorption and eliminat ion. Peak plasma concentration, C(max), was estimated at 4.0 mug/ml an d was estimated to occur at 10.3 h (T(max)) following dosing. The bioa vailability, F, was estimated at 96.5%. Based on the median minimum in hibitory concentrations (MICs) of 0.8 mug/ml reported for Aeromonas sa lmonicida, Vibrio anguillarum and Vibrio salmonicida, plasma concentra tions should remain above the MIC for 36-40 h following a single oral dose of 10 mg florfenicol/kg.