Question

What is the mechanism of action for the drug Omeprazole?

• A. H$_2$ receptor antagonist
• B. Proton pump inhibitor
• C. Anticholinergic agent
• D. Antacid

Hint:

Important Proton Pump Inhibitors (PPIs):

• \textbf{Omeprazole}
• \textbf{Pantoprazole}
• \textbf{Lansoprazole}
• \textbf{Rabeprazole}
• \textbf{Esomeprazole}

Mnemonic: \textbf{“OPLRE”} – Omeprazole, Pantoprazole, Lansoprazole, Rabeprazole, Esomeprazole. \textbf{Mechanism:} Inhibition of the H$^+$/K$^+$–ATPase proton pump in gastric parietal cells.

Answer 1

The Correct Option is B

Concept: Omeprazole is a widely used drug for the treatment of acid-related disorders such as peptic ulcer disease, gastroesophageal reflux disease (GERD), Zollinger–Ellison syndrome, and gastric ulcers. It belongs to a class of drugs known as Proton Pump Inhibitors (PPIs). Proton pump inhibitors work by suppressing the production of gastric acid in the stomach. Omeprazole specifically blocks the enzyme responsible for the final step of acid secretion in the stomach.
Step 1: Understanding the target enzyme.
In the stomach, acid secretion is carried out by the parietal cells. These cells contain an enzyme called the H$^+$/K$^+$–ATPase enzyme, also known as the proton pump. This enzyme exchanges hydrogen ions (H$^+$) with potassium ions (K$^+$) and releases hydrogen ions into the gastric lumen, forming hydrochloric acid (HCl). Omeprazole inhibits this enzyme, thereby reducing gastric acid secretion.
Step 2: Mechanism of action of Omeprazole.

• Omeprazole is a prodrug that becomes activated in the acidic environment of the stomach.
• It binds irreversibly to the H$^+$/K$^+$–ATPase enzyme in parietal cells.
• This blocks the final step of gastric acid secretion.
• As a result, the amount of acid produced in the stomach is significantly reduced.

Because it blocks the final step of acid secretion, Omeprazole is considered highly effective in reducing stomach acidity.
Step 3: Evaluating the options.

• H$_2$ receptor antagonist: Drugs like ranitidine and famotidine belong to this class.
• Proton pump inhibitor: Omeprazole belongs to this class and inhibits H$^+$/K$^+$–ATPase. (Correct)
• Anticholinergic agent: Reduces gastric secretions by blocking acetylcholine.
• Antacid: Neutralizes gastric acid but does not inhibit acid production.

Therefore, the correct answer is: \[ \text{Proton Pump Inhibitor} \]