Effect of salicylate on the fate of [14C]sulfinpyrazone in the rat.

The effect of acetylsalicylic acid (ASA, 100 mg/kg, po) on the fate of [14C]sulfinpyrazone (50 mg/kg, ip) was studied in male Wistar rats. ASA increased the rate of elimination of [14C]sulfinpyrazone-derived radioactivity from the blood during the first 5 h following drug administration. A tissue distribution study at 4 h showed that ASA increased the concentration of radioactivity in the gastrointestinal tract (GIT) and decreased it in the blood, heart, lung, and testis. ASA had little or no effect on the urinary and fecal excretion of sulfinpyrazone metabolites. Biliary elimination of radioactivity was increased from 54.2 +/- 4.7 to 69.6 +/- 1.2% of the dose in the 0- to 5-h period by salicylate (SAL), a major in vivo metabolite of ASA. Bile flow rate was also increased by SAL. An in vitro protein binding study showed that SAL displaced sulfinpyrazone from its binding sites. The results suggested that, in the rat, SAL enhanced the rate of sulfinpyrazone elimination by a combination of its choleretic action and displacement of bound sulfinpyrazone from plasma proteins.