Abstract

Sulfadimethoxine and Ormetoprim in a 5:1 combination (SDMOMP) is approved, by the U.S. FDA, for use in channel catfish (Ictalurus punctatus) and rainbow trout (Oncorhynchus my kiss). This drug combination is also used in an off label manner to treat many other fish species. This study describes the pharmacokinetic parameters of sulfadimethoxine and ormetoprim after intraperitoneal and oral administration in the hybrid striped bass (Morone saxatilis x Morone Chrysops), an important food production species in North Carolina.

Twenty four hybrid striped bass, weighing between 0.456 to 1.2 Kg were used for this study. Each fish had a catheter placed in the sinus venosus to allow repeated blood samples to be retrieved from the free swimming fish. Fish receiving the intraperitoneal dose of the drug (n=12) had an intraperitoneal catheter placed and fish receiving the oral dose of the drug (n=12) had an indwelling gastric feeding tube placed to allow administration of the drug to the free swimming animals. Twelve fish received a single dose of SDM/ONP intraperitoneally and twelve fish received a single dose of SDM/OMP via the gastric feeding tube. A total of three 0.75 ml blood samples were taken from each fish. Each population was sampled at the following time points: 0.25, 2, 4, 6, 8, 12, 18, 24, 36, 48, and 96 hours. The drugs were extracted from the serum using methylene chloride and acetone. SDM and OMP serum concentrations were determined using high performance liquid chromatography (BPLC). The isocratic technique used a mobile phase consisting of 80% 0.1 M phosphate buffer, 15% acetonitrile and 5% methanol, run at a flow rate of 0.5 ml/min over a C-18 column, and drug was detected at 288 nm. Drug concentrations were plotted and pharmacokinetic parameters determined based on a one compartment model using r-strip software.