Schedule dependency of 5-fluorouracil

5-Fluorouracil (5-FU) is cell-cycle specific for its cytotoxicity and has a pharmacokinetic profile characterized by a short, single-dose half-life of 10 to 20 minutes in plasma. Efforts to maximize its clinical efficacy have been directed at overcoming this short half-life. Strategies have included prolonging intracellular exposure by biochemical modulation or administration by infusional schedules, and more recently by chronic oral dosing. A number of clinical trials comparing routes of administration and biochemical modulation of 5-FU are presented in this article. Issues of dose intensity, differing toxicity profiles, and pharmacoeconomics are reviewed.