5- FU nedbrydes yderligere af enzymet dihydropyrimidindehydrogenase (DPD) til det meget mindre toksiske dihydro- 5- fluoruracil (FUH2).
5-FU is further catabolised by the enzyme dihydropyrimidine dehydrogenase (DPD) to the much less toxic dihydro-5-fluorouracil (FUH2).