Oxonic acid is a uricase inhibitor that prevents metabolism and excretion of uric acid and induces embryotoxicity and nephrotoxicity in rats. It is a component of S-1, a mixture containing a prodrug of the antitumor agent 5-fluorouracil (5-FU; ), that suppresses the gastrointestinal toxicity of 5-FU without inhibiting its antitumor activity in rats. Formulations containing oxonic acid have been used to treat gastric, pancreatic, lung, head, neck, and breast carcinomas.
