Comparative pharmacokinetics and bioavailability of oxytetracycline in rainbow trout and chinook salmon

The pharmacokinetics and bioavailabilities of oxytetracycline (OTC) in seawater chinook salmon (Oncorhynchus tshawytscha) and freshwater rainbow trout (Oncorhynchus mykiss) were compared after they were given a single dose of OTC (50 mg/kg) via the i.a. or per os route of administration at 11 degrees C water. At specific time points post-dosing, blood Samples were withdrawn from the fish, extracted by a solid phase extractor and analyzed for OTC with a high performance liquid chromatograph (HPLC). Similar OTC blood concentration-time profiles were found in trout and salmon after they were treated by the same administration route with OTC. A two- and a three-compartment open pharmacokinetic models, respectively, were used to describe the pharmacokinetics of OTC following the per os and i.a. routes of administration. The model-derived pharmacokinetic parameters and the apparent bioavailabilities of OTC also were remarkably similar: the elimination half-life, volume of distribution and oral bioavailability of OTC in chinook salmon were 88.29 h, 0.89 l/kg and 24.84%, respectively; the corresponding values for rainbow trout were 94.22 h, 0.87 l/kg and 30.30%, respectively. Results of the present studies indicate that species difference and salinity as high as 24 parts per thousand do not play an important role in the absorption and elimination of OTC by the salmonids. Moreover, freshwater trout may be used as a model salmonid to study OTC pharmacokinetics in seawater salmon and vice versa. (C) 1998 Elsevier Science B.V.