Interethnic differences in omeprazole metabolism in the two S-mephenytoin hydroxylation phenotypes studied in Caucasians and Orientals

Ther Drug Monit. 1994 Apr;16(2):214-5. doi: 10.1097/00007691-199404000-00018.


Two independent studies showed that the 5-hydroxylation, but not the sulfoxidation, of omeprazole is more rapid in extensive metabolizers (EMs) than in poor metabolizers (PMs) of S-mephenytoin. In Caucasian, Chinese, and Korean PMs, the mean oral clearances were similar and not significantly different (85, 73, and 59 ml h-1 kg-1, respectively). However, 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 Korean EMs (446 ml h-1 kg-1, p < 0.01). The incidence of PMs of S-mephenytoin 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 might explain the higher clearance of omeprazole in Caucasian EMs compared to the clearance of omeprazole in Chinese and Korean EMs of S-mephenytoin.

Publication types

  • Comparative Study

MeSH terms

  • Aryl Hydrocarbon Hydroxylases*
  • Asians* / genetics
  • Cytochrome P-450 CYP2C19
  • Cytochrome P-450 Enzyme System / genetics
  • Humans
  • Mixed Function Oxygenases / genetics
  • Omeprazole / metabolism*
  • Phenotype
  • Whites* / genetics


  • Cytochrome P-450 Enzyme System
  • Mixed Function Oxygenases
  • Aryl Hydrocarbon Hydroxylases
  • CYP2C19 protein, human
  • Cytochrome P-450 CYP2C19
  • Omeprazole