Via enzymet dihydropyrimidin dehydrogenas (DPD) kataboliseras 5- FU vidare till det avsevärt mindre toxiska dihydro- 5- fluorouracil (FUH2). ###>5-FU is further catabolised by the enzyme dihydropyrimidine dehydrogenase (DPD) to the much less toxic dihydro-5-fluorouracil (FUH2).