Tissue residue depletion and recycling of sulfamethazine in swine.

Sulfamethazine was fed to weanling pigs at the rate of 100 g/ton of ration for 98 days to investigate the depletion rate of the drug from the plasma and edible tissues of swine. The mean plasma concentration of sulfamethazine for 21 treated pigs peaked at 10.8 ppm on day 77 of the 98-day treatment period. The concentration of sulfamethazine in kidney, liver, skeletal muscle, and subcutaneous fat was at or below 0.1 ppm within 7 days after withdrawal of medicated feed. Depletion of sulfamethazine from the tissues and plasma of the treated pigs plotted on a semilogarithmic graph. Six of seven unoccupied by the treated pigs accumulated drug residues in their kidney and liver tissues. Sulfamethazine concentrations in these tissues were at or above 0.1 ppm in 5 to 14 days.