Which statement best describes the mechanism of action of proton pump inhibitors?

• A. They inhibit the proton pump in gastric parietal cells to reduce acid production
• B. They block H2 receptors
• C. They neutralize existing stomach acid
• D. They coat the stomach lining

Answer: (A)

Proton pump inhibitors work by blocking the final step of acid secretion in the stomach. They target the proton pump (H+/K+-ATPase) in gastric parietal cells, irreversibly inhibiting it so hydrogen ions are not pumped into the stomach lumen. Because the pump is inactivated until new pumps are made, acid production drops and remains suppressed for an extended period, even after the drug is cleared. This mechanism is distinct from H2 receptor blockers, which stop histamine from stimulating acid release; from antacids, which neutralize existing acid; and from agents that coat the stomach lining. Therefore, inhibiting the proton pump to reduce acid production best describes their action.