Esomeprazole: potent acid suppression in the treatment of acid-related disorders

Pharmacokinetics and pharmacodynamics of the proton pump inhibitors

Proton pump inhibitor (PPI) is a prodrug which is activated by acid. Activated PPI binds covalently to the gastric H⁺, K⁺-ATPase via disulfide bond. Cys813 is the primary site responsible for the inhibition of acid pump enzyme, where PPIs bind. Omeprazole was the first PPI introduced in market, followed by pantoprazole, lansoprazole and rabeprazole. Though these PPIs share the core structures benzimidazole and pyridine, their pharmacokinetics and pharmacodynamics are a little different. Several factors must be considered in understanding the pharmacodynamics of PPIs, including: accumulation of PPI in the parietal cell, the proportion of the pump enzyme located at the canaliculus, de novo synthesis of new pump enzyme, metabolism of PPI, amounts of covalent binding of PPI in the parietal cell, and the stability of PPI binding. PPIs have about 1hour of elimination half-life. Area under the plasmic concentration curve and the intragastric pH profile are very good indicators for evaluating PPI efficacy. Though CYP2C19 and CYP3A4 polymorphism are major components of PPI metabolism, the pharmacokinetics and pharmacodynamics of racemic mixture of PPIs depend on the CYP2C19 genotype status. S-omeprazole is relatively insensitive to CYP2C19, so better control of the intragastric pH is achieved. Similarly, R-lansoprazole was developed in order to increase the drug activity. Delayed-release formulation resulted in a longer duration of effective concentration of R-lansoprazole in blood, in addition to metabolic advantage. Thus, dexlansoprazole showed best control of the intragastric pH among the present PPIs. Overall, PPIs made significant progress in the management of acid-related diseases and improved health-related quality of life.

Intragastric acidity during administration of generic omeprazole or esomeprazole - a randomised, two-way crossover study including CYP2C19 genotyping

BACKGROUND

Generic omeprazole has been approved in many countries for the treatment of acid-related gastrointestinal disorders. However, clinical studies comparing generic to original proton pump inhibitors are limited.

AIMS

To compare the effect of generic omeprazole 20 mg/day with esomeprazole 20 mg/day on intragastric acidity and to investigate the influence of the CYP2C19 metabolizer status.

METHODS

In this randomised, single-blinded, two-way crossover study, 24 healthy Helicobacter pylori-negative subjects, received generic omeprazole (Omep; Hexal AG, Holzkirchen, Germany) 20 mg once daily or esomeprazole 20 mg once daily for five consecutive days. Twenty-four-hour intragastric pH was recorded on day 5 of each treatment. CYP2C19 status was determined by polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

Over all, there were no statistically significant differences between generic omeprazole and esomeprazole with respect to median intragastric pH (3.5 and 3.9, P = 0.07), the total hours with intragastric pH >4 (10.4 and 11.3, P = 0.29), and during upright (9.6 and 9.1, P = 0.77) or supine (2.2 and 2.2, P = 0.94) position. However, in CYP2C19 rapid metabolizers, esomeprazole was superior to omeprazole, with the percentage of time with intragastric pH >3.0 and pH >3.5 being higher with esomeprazole than with generic omeprazole [Δ = 9% (P = 0.026) and Δ = 8% (P = 0.046), respectively].

CONCLUSIONS

Overall, generic omeprazole 20 mg appears to provide a similar intragastric acid control when compared with esomeprazole 20 mg. However, esomeprazole might be advantageous in subjects with a rapid CYP2C19 metabolizer status.