Deposition kinetics, metabolism and urinary excretion of sulfathiazole following oral administration in sheep.

Deposition kinetics, metabolism and urinary excretion of sulfathiazole were investigated in German black head sheep following single oral administration (100 mg/kg). Kinetic evaluation of plasma levels was performed using a two-compartment best fit model. Sulfathiazole is significantly metabolized to N4-acetyl metabolite in the rumen fluid. The drug is very poorly absorbed since the minimum effective concentration in plasma was not attained at any time following oral administration. The prolonged elimination half-life in sheep may be due to a low rate of drug absorption from the rumen and gastro-intestinal tract. Sulfathiazole was mainly excreted in the urine as free drug and N4-acetyl metabolite.