Stereospecific analysis of omeprazole in human plasma as a probe for CYP2C19 phenotype

Omeprazole is a class referred to as proton pump inhibitor; it acts to regulate acid production in the stomach and is used to treat various acid-related gastrointestinal disorders. In the liver, it is metabolized to varying degrees by several cytochrome P-450 (CYP) isoenzymes which are further categorized into subfamilies of related polymorphic gene products. The metabolism of omeprazole is to a large extent dependent on CYP3A4 and CYP2C19. Omeprazole is metabolized to two major metabolites, 5-hydroxyomeprazole (CYP2C19) and omeprazole sulfone (CYP3A4). Minor mutations in CYP2C19 affect its activity in the liver and, in turn, the metabolic and pharmacokinetic profiles of omeprazole. The frequency of CYP2C19 poor metabolizers in population of Asian descent has been reported to range from 10 to 20%. Accordingly, results from population studies indicate that omeprazole can be used as a probe drug for phenotyping CYP2C19. The optical isomers of omeprazole show a clear difference in their metabolism by human liver microsomes. This study demonstrates the stereospecific analysis of omeprazole in human plasma as a probe drug of CYP2C19 phenotyping. The chiral separation of omeprazole was achieved on a chiral column with circular dichroism (CD) detection and LC/MS. A good resolution of enantiomers was obtained. The column used for chiral separation was CHIRALPAK AD-RH column (4.6 x 150 mm) using phosphate buffer and (or ammonium acetate) acetonitrile as an eluent. After a single oral dose of omeprazole (20 mg), the plasma concentrations of the separate enantiomers of omeprazole were determined for 3.5 h after drug intake. The present study is useful because of the part polymorphism plays in the therapeutic effectiveness of proton pump inhibitors during the treatment of acid-related diseases.