Comparison of the pharmacokinetics and pharmacodynamics of S-1 between Caucasian and East Asian patients

Abstract

S-1 is an oral fluoropyrimidine anti-neoplastic agent that is converted by CYP2A6 to 5-fluorouracil (5FU). We prospectively studied the pharmacokinetics and pharmacodynamics of S-1 in two groups of East Asian and Caucasian patients with solid malignancy refractory to standard chemotherapy, or for which 5FU was indicated, to elucidate differences in relation to CYP2A6 genotype and phenotype. S-1 was given orally at 30mg/m2 b.i.d. for 14days every 21days. Dose normalized AUC0-48h for tegafur (P=0.05) and gimeracil (P=0.036) were higher in East Asians; conversely, AUC0-48h of fluoro-β-alanine was higher in Caucasians (P=0.044). Exposure to 5FU was similar in both groups (P=0.967). Mean cotinine:nicotine ratio was 54% higher in the Caucasian group (P=0.03), and correlated with oral clearance of tegafur (r=0.59; P=0.002). Grade 3/4 gastrointestinal toxicities were more common in Caucasians than Asians (21%vs 0%). Treatment with S-1 yields no significant difference in 5FU exposure between Caucasians and East Asians. © 2010 Japanese Cancer Association.