*3.1.1 5-Fluorouracil (5-FU)*

5FU is an antimetabolite drug that inhibits DNA and RNA synthesis by acting as a false substrate in purine and pyrimidine synthesis thereby interfering in the S phase of the tumor cell cycle. It is metabolized by the rate limiting enzyme dihydropyrimidine dehydrogenase. The main toxicities are related to mucosal inflammation and this presents clinically as mucositis, stomatitis and diarrhea. It can also cause nausea and myelosuppression. Rarely, it can cause cardiotoxicity presumably by inducing coronary artery spasm.
