Protracted intravenous regimens of fluorouracil (5-FU) may be superior and better tolerated than intravenous bolus dosing. An effective oral regimen would allow a protracted course of 5-FU without the need for central venous lines and the associated increase in complications. Approximately 85% of 5-FU is degraded by dihydropyrimidine dehydrogenase (DPD); inhibition of this enzyme pathway can increase the amount of circulating 5-FU. Two oral fluoropyrimidines commonly referred to as DPD inhibitory fluoropyrimidines, or DIFs, UFT plus leucovorin (LV) and S-1 are reviewed herein. These agents represent an approach to more convenient, less toxic 5-FU therapy. In two multicenter, randomized, phase III trials in patients with advanced colorectal cancer, UFT/LV produced equivalent activity compared with intravenous 5-FU/LV but with significantly less major toxicity. The predominant side effect of UFT, diarrhea, is generally self-limited and easily managed. Myelosuppression and hand-foot syndrome were rarely noted in the schedules used in these trials. S-1 has demonstrated promising activity in phase II trials conducted in patients with gastric, colorectal, breast, and head and neck cancers. Ongoing trials are defining the roles of these agents in a variety of malignancies.
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