5-Fluorouracil is an antipyrimidine drug. It is white or white crystalline powder. It must be transformed into 5-fluorodeoxyuridine nucleotide by enzymes to have anti-tumor activity, and inhibit DNA synthesis by inhibiting thymidine nucleotide synthase. This enzyme may also transfer the carbon unit of formyltetrahydrofolic acid to deoxyuridine monophosphate to synthesize thymidine monoacid. It also inhibits the synthesis of RNA. Clinically, it is effective in the treatment of many kinds of tumors, such as digestive tract tumors, breast cancer, ovarian cancer, chorioepithelial cancer, cervical cancer, bladder cancer, liver cancer, skin cancer, etc. Especially for digestive tract cancer and other solid tumors, it can be injected intravenously or intravenously, and oral absorption is incomplete.
Oral absorption of 5-Fluorouracil is incomplete and unpredictable, so it is injected and distributed rapidly to all tissues of the whole body: cerebrospinal fluid and tumor tissue after intravenous injection. As mentioned above, 5-FU can only be converted into active nucleotide metabolites in vivo. Metabolic degradation can occur in many tissues, especially in the liver. Under the action of 5-FU dihydropyrimidine reductase in liver, intestinal mucosa and other tissues, the pyrimidine ring was reduced to 5-fluoro-5,6-dihydropyrimidine and inactivated. If the enzyme is absent due to inheritance, the sensitivity to the drug will be greatly increased, and very few people show strong toxicity to 5-FU in common dosage due to the lack of the enzyme. The final metabolite of 5-FU is alpha-fluoro-beta-alanine. The plasma concentration of 5-FU could reach 0.1-0.3 by rapid intravenous injection.