Pharmacokinetics Of Oxytetracycline In Yellow Perch (Perca flavescens) As Determined By Plasma Concentration Following Different Routes Of Administration     Brent C. Bowden and Stephen A. Smith   Aquatic Medicine Laboratory, Department of Biomedical Sciences and Pathobiology, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061     Oxytetracycline (OTC) is one of two antimicrobials currently available and approved by the U.S. Food and Drug Administration for use as a chemotherapeutic in food fish. This broad-spectrum antimicrobial is widely used in the aquaculture industry not only because of the limited availability of other approved drugs but also because OTC has a low order of toxicity and a high ability to readily disperse into blood and most tissues. Recent pharmacokinetic studies of OTC have been conducted in the cold-water species of rainbow trout, Atlantic salmon, chinook salmon and tench, and the warm water species of African catfish, carp, and pacu. However, no pharmacokinetic studies have been conducted on a cool water species such as yellow perch (Perca flavescens). The yellow perch is a cool water game and commercial species with high aquaculture potential. Using a modification of a high performance liquid chromatographic technique that utilizes micropartition filtering, the plasma OTC concentrations in yellow perch were determined following intraperitoneal (i.p.), intramuscular (i.m.), per os (p.o.), and intravascular (i.v.) administration at a dose of 50 mg/kg body weight. Plasma concentrations were also evaluated in yellow perch exposed to a static 48 h oxytetracycline bath (100 mg/l). The terminal half-lives (t1/2) for OTC following the i.p., i.m., p.o., and i.v. administrations (112.4, 123.8, 50.2, and 27.6 h respectively) were significantly longer than any of the published OTC studies in fish to date. However, the times of maximum OTC concentration (tmax) for the i.p., i.m., and the p.o. administrations (2, 4, 15 h respectively) occurred relatively early in the plasma concentration-time curves. This suggests, that in yellow perch, OTC is initially absorbed very rapidly but excreted relatively slowly. Values for the area under the plasma concentration-time curves (AUC0-›¥) were 1718, 2658, 383 and 134 µg·h/ml respectively following i.p., i.m., p.o. and i.v. administration. No OTC was detected in the plasma of yellow perch following the water bath route of exposure.