Which of the following is an H2 receptor antagonist?

The selection of cimetidine as the H2 receptor antagonist is based on its pharmacological action. H2 receptor antagonists work by blocking histamine at the H2 receptors of the gastric parietal cells, which reduces gastric acid secretion. Cimetidine is one of the first medications introduced in this class and is commonly used to treat conditions such as peptic ulcers and gastroesophageal reflux disease (GERD) due to its ability to effectively lower acid production in the stomach.

Omeprazole, on the other hand, is a proton pump inhibitor, which functions by irreversibly blocking the hydrogen-potassium ATPase enzyme system in the gastric parietal cells, thereby inhibiting gastric acid secretion but through a different mechanism than H2 antagonists. Misoprostol is a prostaglandin E1 analog, which does not act on H2 receptors but instead protects the gastric mucosa and stimulates gastric mucus production. Metoclopramide primarily serves as a prokinetic agent and antiemetic, increasing gastrointestinal motility and facilitating gastric emptying, without having an antagonistic effect on H2 receptors.

Thus, cimetidine is recognized as an H2 receptor antagonist due to its specific role in blocking acid production through