Studies on the metabolism of 1-(2-tetrahydrofuryl)-5-fluorouracil and uracil co-administered orally to tumor-bearing rats.

The metabolism of 1-(2-tetrahydrofuryl)-5-fluorouracil (FT) plus uracil (1:4, UFT) was compared with that of FT alone and that of uracil alone in tumor-bearing rats by using 3H-tracer. After oral administration of UFT, both FT and uracil were rapidly absorbed and no interaction of their absorptions was observed. The levels of 5-fluorouracil (5-FU) in the blood and tissues and the excretion of 5-FU in the urine of rats given UFT were temporarily higher, and the levels of alpha-fluoro-beta-ureidopropionic acid (a catabolic metabolite of 5-FU) in almost all tissues were lower than in rats given FT. The levels of 5-FU, 5-fluorouridine, and fluoronucleotides increased more in the tumors than in normal tissues of rats given UFT, but not in those given FT. The metabolism of uracil administered exogenously as UFT was not influenced by 5-FU or its metabolites derived from FT.