Hydrolysis of salicyluric acid in intestinal microorganisms and prolonged blood concentration of salicylic acid following rectal administration of salicyluric acid in rats.

The blood concentrations of salicyluric acid and salicylic acid following oral, intravenous, intracecal and rectal administration of salicyluric acid were determined in rats. After oral administration of salicyluric acid, salicyluric acid was rapidly absorbed. Salicylic acid was detected at low concentration. Following intravenous administration of salicyluric acid, salicyluric acid was detected in the blood and was rapidly eliminated. A trace amount of salicylic acid was detected, suggesting that systemic deconjugation of glycine was involved. Furthermore, in vitro incubation of salicyluric acid with contents of the gut showed that the major source of the hydrolysis was the hind gut. Immediate and very extensive salicylic acid formation in the cecum was found following intracecal administration of salicyluric acid. The blood concentration of salicylic acid was maintained at 2.6-4.0 micrograms/ml from 4 to 12 h following rectal administration of salicyluric acid (10 mg/kg: salicylic acid equivalent). Species difference in the metabolic fate of salicyluric acid in rats and rabbits reported previously is discussed.