INTERETHNIC DIFFERENCES IN OMEPRAZOLE METABOLISM IN THE 2 S-MEPHENYTOIN HYDROXYLATION PHENOTYPES STUDIED IN CAUCASIANS AND ORIENTALS

Two independent studies showed that the 5-hydroxylation, but not the s ulfoxidation, of omeprazole is more rapid in extensive metabolizers (E Ms) than in poor metabolizers (PMs) of S-mephenytoin. In Caucasian, Ch inese, and Korean PMs, the mean oral clearances were similar and not s ignificantly different (85, 73, and 59 ml h-1 kg-1, respectively). How ever, the geometric mean clearance in Caucasian EMs (950 ml h-1 kg-1) was higher than in both Chinese EMs (426 ml h-1 kg-1, p < 0.05) and Ko rean EMs (446 ml h-1 kg-1, p < 0.01). The incidence of PMs of S-mephen ytoin is higher in Chinese (14.6%) and Koreans (12.6%) than in Swedish Caucasians (3.3%). Therefore, the proportion of heterozygous compared to homozygous EMs is higher in Orientals than in Caucasians. This mig ht explain the higher clearance of omeprazole in Caucasian EMs compare d to the clearance of omeprazole in Chinese and Korean EMs of S-mephen ytoin.