omeprazole, a substituted benzimidazole, is a potent inhibitor of gastric acid secretion. Omeprazole decreases gastric acid secretion by blocking
the H1,K1-adenosine triphosphatase (acid pump)in the secretory membrane of the parietal cell. This enzyme catalyzes the exchange of hydrogen ions for potassium ions in the final step of hydrochloric acid production by the parietal cell. Therefore,omeprazole is characterized as an acid-pump inhibitor and blocks gastric acid secretion irrespective of stimulus.