Disposition of sulfonamides in food-producing animals: concentrations of sulfamethazine and its metabolites in plasma, urine, and tissues of lambs following intravenous administration.

A sensitive, precise, and efficient analytical method for sulfamethazine in the liver, kidney, heart, skeletal muscle, and fat of lambs is reported. The method involves freezing cubed tissue in liquid nitrogen, powdering the frozen tissue in a liquid nitrogen-cooled blender, and extracting the tissue on a sodium sulfate column with chloroform:acetone. A thin-layer chromatographic procedure capable of separating and quantitating sulfamethazine and 3 metabolites (acetyl, hydroxylated, and polar conjugate(s) in lamb urine is also reported. Sulfamethazine was administered intravenously (107.25 mg/kg body weight) to 14 cross-bred ewe lambs. The concentration of sulfamethazine in plasma and tissues and sulfamethazine and its metabolites in urine were determined in samples collected at specific postdosing times. The concentration of sulfamethazine in plasma exceeded 5 mg/100 ml for 18 to 24 hours after drug administration. The excretion of diazotizable materials in the urine was essentially complete at the 60th hour after dosing. The drug was excreted in the urine as sulfamethazine, a hydroxylated metabolite, acetylsulfamethazine, and polar conjugate(s). Tissue concentrations of the drug were greatest in the kidney and less (in decreasing quantities) in liver, heart, skeletal muscle, body fat, and omental fat.