Sulfatroxazole: pharmacokinetics, metabolism and urinary excretion in goats and pigs

The disposition of sulfatroxazole (STZ) has been studied in goats and pigs after intravenous administration of a single dose. The percentage of protein-binding decreased with increasing plasma concentration in both species. At 100 micrograms/ml about 85% was bound to plasma proteins in goats, while the corresponding value was only 55% in pigs. Two metabolites of STZ were isolated from urine and identified as N4-acetyl-STZ and 3-sulfanilamido-4-methyl-5-hydroxy-methyl-isoxazole (5'-OH-STZ). The goats excreted about 80% of the dose in urine. The majority (64%) was excreted as unchanged STZ, while N4-acetyl-STZ and 5'-OH-STZ made up 19% and 18%, respectively. The pigs excreted 95% of the dose in urine. Unchanged STZ amounted to 30% and N4-acetyl-STZ to 70% of the urinary excretion in pigs, while there were only traces of 5'-OH-STZ.