Determination of CYP2C19 phenotype in black Americans with omeprazole: Correlation with genotype

Jacqueline S. Marinac, John D. Balian, John W. Foxworth, Sandra K. Willsie, Jennifer C. Daus, Renius Owen, David A. Flockhart

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Background: Our objective was to study omeprazole as a single-dose oral probe in the determination of CYP2C19 phenotype in black subjects and to determine the correlation between phenotype and genotype. Methods: This single-dose, open-label outpatient study was conducted at a community-based, university-affiliated teaching hospital outpatient clinic. Study subjects were 100 healthy, unrelated black adults (age range, 18 to 50 years) who were receiving no medications. Baseline omeprazole and 2-hour postingestion omeprazole and 5'-hydroxyomeprazole concentrations were measured for phenotype determination. Identification of CΥP2C19(m1) genotypes were performed with use of the polymerase chain reaction. Results: Results were obtained for 28 men and 72 women. Ninety-eight subjects were found to be phenotypically extensive metabolizers and two to be poor metabolizers (one man; one smoker). Genotype determination revealed that the two poor metabolizers of omeprazole were homozygous for a single base pair mutation (m1/m1) in exon 5 of CΥP2C19. Twenty-eight of the extensive metabolizers were heterozygous (m1/wt) and the remaining 70 were homozygous (wt/wt). No side effects were reported. Conclusions: The 2% prevalence rate of poor CYP2C19 metabolizers in this healthy black population residing in the Midwestern United States is similar to that reported in white subjects and in the Shona population of Zimbabwe but much less than in Asian subjects. Omeprazole is a safe and specific probe of the CYP2C19 enzyme system that correlates well with genotype.

Original languageEnglish (US)
Pages (from-to)138-144
Number of pages7
JournalClinical Pharmacology and Therapeutics
Issue number2
StatePublished - Aug 1 1996


ASJC Scopus subject areas

  • Pharmacology
  • Pharmacology (medical)

Cite this

Marinac, J. S., Balian, J. D., Foxworth, J. W., Willsie, S. K., Daus, J. C., Owen, R., & Flockhart, D. A. (1996). Determination of CYP2C19 phenotype in black Americans with omeprazole: Correlation with genotype. Clinical Pharmacology and Therapeutics, 60(2), 138-144.