About Omeprazole Proton Pump Inhibitor, Substituted Benzimidazole, Anti-secretory,antiulcer. Mechanism of Action of Omeprazole Omeprazole is a proton pump inhibitor and it is a prodrug. After administration it diffuses in to the parietal cell of the stomach and accumulates in the secretory canaliculi. In the acidic medium Omeprazole is converted to sulfenamide. This sulfenamide covalently interacts with sulfhydryl (SH) group in the proton pump (H+ K+ATPase) and inhibits the exchange of extracellular K+ for intracellular H+ ion. Omeprazole irreversibly inhibits proton pumps activity and decreases gastric acid secretion.