Two dosages of oral fluoropyrimidine S-1 of 35 and 40 mg/m² bid: Comparison of the pharmacokinetic profiles in Korean patients with advanced gastric cancer

Objective: In this study, we compared the pharmacokinetic profiles of 5-fluorouracil (5-FU), tegafur, 5-chloro-2,4-dihydroxypyridine (CDHP) and potassium oxonate (Oxo) after administration of S-1 at 35 or 40 mg/m. ² bid for 28 consecutive days, in Cycles 1 and 3, in patients with advanced gastric cancer. Methods: Three patients were enrolled for each dosage. S-1 dosage was assigned based on body surface area (BSA), which is different from the Japanese dosing system. The median daily dose per BSA was 76 mg/m. ², ranging from 70 to 88 mg/m. ². Results: Plasma levels of 5-FU, tegafur, CDHP and Oxo at 4 h post-dose reached steady-state on day 8. The estimated steady-state level was dependent on S-1 dosage. There were no intercyclic differences of pre-dose and 4 h post-dose levels between Cycles 1 and 3, implying no cumulative effect of S-1 was shown probably due to 2-week drug-resting period. Pharmacokinetic profiles on day 28 were similar to previous Japanese report. C_max and AUC_{0-48 h} values of each S-1 component increased depending on S-1 dosage. Pharmacokinetic parameters were not correlated with tumor response or toxicity. Conclusions: We suggest that these pharmacokinetic profiles of Asian population could provide a basis for schedule optimization and for additional studies on interaction with other antitumor drugs.