Fixed dosing and pharmacokinetics of S-1 in Japanese cancer patients with large body surface areas

Background: S-1 is an oral anticancer agent that combines tegafur (FT) with 5-chloro-2,4-dihydroxypyridine (CDHP) and potassium oxonate. The recommended initial dose of S-1 is 120 mg/day for patients with a body surface area (BSA) of ≥1.5 m 2 in Japan. Methods: We examined the effects of using this fixed dose on the pharmacokinetics of FT, CDHP, and active 5-fluorouracil (5-FU) on the basis of actual BSA. The pharmacokinetics was compared between patients with a BSA of 1.5-1.75 m 2 and those with a BSA of ≥1.75 m 2 . Results: The median areas under the time-concentration curves (AUCs) of 5-FU and CDHP were significantly lower in patients with a BSA of ≥1.75 m 2 than in those with a BSA of 1.5-1.75 m 2 (P = 0.005 and 0.006, respectively; Mann-Whitney U-test). There was no difference between the groups in the median AUC of FT. Conclusion: Systemic exposure to 5-FU is significantly lower in Japanese cancer patients with a large BSA of >1.75 m 2 who received the recommended fixed dose of S-1.