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 rai nbow 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 adminis tration at 11 degrees C water. At specific time points post-dosing, bl ood Samples were withdrawn from the fish, extracted by a solid phase e xtractor and analyzed for OTC with a high performance liquid chromatog raph (HPLC).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 m odels, respectively, were used to describe the pharmacokinetics of OTC following the per os and i.a. routes of administration. The model-der ived 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 8 8.29 h, 0.89 l/kg and 24.84%, respectively; the corresponding values f or rainbow trout were 94.22 h, 0.87 l/kg and 30.30%, respectively. Res ults of the present studies indicate that species difference and salin ity as high as 24 parts per thousand do not play an important role in the absorption and elimination of OTC by the salmonids. Moreover, fres hwater trout may be used as a model salmonid to study OTC pharmacokine tics in seawater salmon and vice versa. (C) 1998 Elsevier Science B.V.