5-Fluorouracil

5-Fluorouracil is an S phase, specific uracil analogue that can be activated with two major intracellular pathways: (a) sequential phosphorylation and incorporation into RNA or (b) activation to 5-fluorodeoxyuridine monophosphate, which blocks both the enzyme thymidylate synthase and the conversion of uridine into thymidine compounds. Cells are depleted of thymidine and cannot synthesize DNA. Many other drugs have been shown to interact with 5-FU, and trials aimed at increasing its activity by means of modulating its intracellular metabolism have been conducted. The most important side effects are myelosuppression, mucositis, diarrhea, dermatitis, and cardiac toxicity. Used as a single-agent intravenous bolus to treat patients with head and neck cancer, 5-FU has limited activity. A response rate of 13% was found in one large, randomized trial (13). 5-Fluorouracil can be substantially more active administered in a 5-day continuous infusion and clearly adds to the response rate of cisplatin.

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