title: Tissue distribution and biotransformation of potassium oxonate after oral administration of a novel antitumor agent (drug combination of tegafur, 5-chloro-2,4-dihydroxypyridine, and potassium oxonate) to rats.
abstract: S-1, a new oral 5-fluorouracil (5-FU)-derivative antitumor agent, is composed of tegafur, 5-chloro-2,4-dihydropyridine, and potassium oxonate (Oxo). Oxo, which inhibits the phosphorylation of 5-FU, is added to reduce the gastrointestinal (GI) toxicity of the agent. In this study, we investigated the tissue distribution and the metabolic fate of Oxo in rats after oral administration of S-1. Oxo was mainly distributed to the intracellular sites of the small intestines in a much higher concentration than 5-FU, but little distributed to other tissues, including tumorous ones in which 5-FU was observed after oral administration of S-1. Plasma concentration-time profiles of Oxo and its metabolites after i.v. and oral administration of S-1 revealed that Oxo was mainly converted to cyanuric acid in the GI tract. Furthermore, the analysis of drug-related radioactivity in GI contents and in vitro studies suggested that Oxo was converted to cyanuric acid by two routes, the first being direct conversion by the gut flora in the cecum, and the second, conversion by xanthine oxidase or perhaps by aldehyde oxidase after degradation to 5-azauracil (5-AZU) by the gastric acid. These results indicate that, although a part of the administered Oxo was degraded in the GI tract, Oxo was mainly distributed to the intracellular sites of the small intestines in a much higher concentration than 5-FU and that little was distributed to other tissues, including tumors. We conclude that this is the reason why Oxo suppresses the GI toxicity of 5-FU without affecting its antitumor activity.
authors.affiliation: Pharmacokinetics Research Laboratory, Tokushima Research Center, Taiho Pharmaceutical Co., Ltd., Tokushima, Japan. kuni-yosisue@taiho.co.jp
authors.forename: K
authors.initials: K
authors.lastname: Yoshisue
authors.forename: H
authors.initials: H
authors.lastname: Masuda
authors.forename: E
authors.initials: E
authors.lastname: Matsushima
authors.forename: K
authors.initials: K
authors.lastname: Ikeda
authors.forename: S
authors.initials: S
authors.lastname: Nagayama
authors.forename: Y
authors.initials: Y
authors.lastname: Kawaguchi
mesh_terms: D000284:Administration, Oral; D000493:Allopurinol / Q000494:pharmacology; D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000378:metabolism / Q000493:pharmacokinetics*; D019540:Area Under Curve; D001711:Biotransformation; D002250:Carbon Radioisotopes; D002746:Chlorpromazine / Q000494:pharmacology; D004338:Drug Combinations; D004365:Drugs, Chinese Herbal / Q000494:pharmacology; D005472:Fluorouracil / Q000097:blood / Q000378:metabolism; D006035:Glycyrrhiza; D007421:Intestine, Small / Q000378:metabolism; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism; D010094:Oxonic Acid / Q000097:blood / Q000378:metabolism / Q000493:pharmacokinetics*; D029596:Paeonia; D011725:Pyridines / Q000097:blood / Q000378:metabolism / Q000493:pharmacokinetics*; D051381:Rats; D011919:Rats, Inbred Strains; D012517:Sarcoma, Yoshida / Q000188:drug therapy / Q000378:metabolism; D005641:Tegafur / Q000097:blood / Q000378:metabolism / Q000493:pharmacokinetics*; D014018:Tissue Distribution; D014227:Triazines / Q000097:blood / Q000378:metabolism; D014498:Uracil / Q000031:analogs & derivatives* / Q000378:metabolism; D014969:Xanthine Oxidase / Q000378:metabolism
chemical_list: D000964:Antimetabolites, Antineoplastic; D002250:Carbon Radioisotopes; D004338:Drug Combinations; D004365:Drugs, Chinese Herbal; D011725:Pyridines; D014227:Triazines; C038462:shakuyaku-kanzoh-toh; C079198:S 1 (combination); D005641:Tegafur; D014498:Uracil; D010094:Oxonic Acid; D000493:Allopurinol; D014969:Xanthine Oxidase; C039856:5-azauracil; C004632:cyanuric acid; D005472:Fluorouracil; D002746:Chlorpromazine