Disposition of sulfonamides in food-producing animals: pharmacokinetics of sulfathiazole in sheep.

Plasma and urine data on sheep following administration of sulfathiazole as single intravenous and oral doses were examined. A one-compartment open model was developed to describe the pharmacokinetics of sulfathiazole in sheep. The drug was rapidly eliminated, primarily by renal excretion of unchanged sulfathiazole and metabolism to acetyl sulfathiazole, with a biological half-life of 1.3 hours. Sulfathiazole was absorbed slowly (half-life, 18 hours) and relatively completely (73%) after oral administration in solution.