Sulfadimethoxine pharmacokinetics and metabolism in the channel catfish (Ictalurus punctatus)

The pharmacokinetics of sulfadimethoxine (SDM) blood clearance, gastrointestinal absorption and tissue distribution and elimination were determined in channel catfish (Ictalurus punctatus) after intravenous and oral dosing using radiolabelled SDM. Blood clearance of SDM in catfish was rapid compared to mammals when the drug was given iv. Results from in vitro equilibrium dialysis studies suggest that this is due to a lower binding of SDM to plasma proteins in fish (18.4%) compared to mammalian species (60-88%). Results from oral dose studies indicated that SDM is readily absorbed from the gastrointestinal tract in channel catfish and distributes rapidly to body tissues, primarily the muscle. With time, concentrations of SDM in muscle decrease and the drug accumulates in the bile, primarily as the N-acetyl-metabolite.