The sodium salt of the prodrug rabeprazole, a substituted benzimidazole proton pump inhibitor, with potential anti-ulcer activity. After protonation, accumulation, and transformation to the active sulfenamide within the acidic environment of gastric parietal cells, rabeprazole selectively and irreversibly binds to and inhibits the H+, K+ATPase (hydrogen-potassium adenosine triphosphatase) enzyme system located on the parietal cell secretory surface, inhibiting gastric acid secretion.