Elimination of sulfamethazine residues from swine.

Tissue concentrations of sulfamethazine in swine fed the drug at the rate of 500 g/ton of ration (550 g/1,000 kg) for a 30-day period depleted to 0.1 ppm or less within 4 to 10 days after withdrawal of medicated feed. Depletion from the tissues and plasma of treated pigs showed a linear relationship with time when the concentrations were plotted on a semilogarithmic graph. Six untreated pigs that were placed on bedding in pens formerly occupied by the treated group developed tissue residues at or above 0.1 ppm sulfamethazine; the mean plasma concentration of sulfamethazine reached 2.8 ppm by day 15.