Effect of dose-escalation of 5-fluorouracil on circadian variability of its pharmacokinetics in Japanese patients with Stage III/IVa esophageal squamous cell carcinoma

Objective: The effects of dose-escalation of 5-fluorouracil (5-FU) on the clinical outcome and pharmacokinetics of 5-FU were investigated in Japanese patients with Stage III/IVa esophageal squamous cell carcinoma.Methods: Thirty-five patients with Stage III/IVa were enrolled, who were treated with a definitive 5-FU/cisplatin-based chemoradiotherapy. A course consisted of continuous infusion of 5-FU at 400 mg/m²/day (the standard dose group, N=27) or 500-550 mg/m²/day (the high dose group, N=8) for days 1-5 and 8-12, infusion of cisplatin at 40 mg/m²/day on days 1 and 8, and radiation at 2 Gy/day on days 1 to 5, 8 to 12, and 15 to 19, with a second course repeated after a 2-week interval. Plasma concentrations of 5-FU were determined by high performance liquid chromatography at 5:00 PM on days 3, 10, 38 and 45, and at 5:00 AM on days 4, 11, 39 and 46.Results and conclusions: No patient with Stage IVa achieved a complete response in the standard dose group, whereas a complete response was observed at a rate of 50% in the high dose group, and this can be explained by a higher plasma concentration of 5-FU. The circadian rhythm in the concentrations found at the standard dose was not observed for a higher dose.