Pharmacology of H2 Receptor Antagonists


H2 receptor antagonists, also known as H2 blockers, are a class of medications that are commonly used to reduce the production of stomach acid. They work by blocking histamine action on H2 receptors found in the gastric parietal cells, thereby inhibiting gastric acid secretion. Examples of H2 receptor antagonists include Cimetidine, Ranitidine, Famotidine, and Nizatidine.

Mechanism of Action

H2 receptor antagonists work by selectively blocking the histamine H2 receptors on the basolateral (blood-facing) membranes of the parietal cells in the stomach. This prevents histamine from binding to these receptors, thereby inhibiting the secretion of gastric acid.

Here’s a flowchart illustrating the mechanism of action of H2 antagonists:

Mechanism of Action of H2 Antagonists
Mechanism of Action of H2 Antagonists


  1. Stimulation of H2 receptors leads to an increase in gastric acid secretion.
  2. H2 Antagonists result in the blockage of H2 receptors.
  3. This blockage causes a reduction in gastric acid secretion.


Absorption, Distribution, Metabolism, and Excretion (ADME)

H2 receptor antagonists are well absorbed from the gastrointestinal tract and undergo first-pass metabolism in the liver. They are distributed throughout the body, including the central nervous system (CNS). These drugs are metabolized in the liver and excreted in the urine.

Pharmacological Actions

H2 receptor antagonists have several pharmacological actions on various systems:

  • Gastrointestinal System: They reduce gastric acid secretion and volume of gastric juices, thereby providing relief from heartburn and promoting the healing of ulcers.
  • Cardiovascular System: They have minimal effects on the cardiovascular system.
  • Central Nervous System: They can cross the blood-brain barrier and may cause side effects such as confusion and dizziness, especially in the elderly.

Therapeutic Uses

H2 receptor antagonists are used in the treatment of several conditions, including:

Side Effects

Common side effects of H2 receptor antagonists include:

  • Headache
  • Dizziness
  • Diarrhea
  • Muscle pain


H2 receptor antagonists are contraindicated in patients with known hypersensitivity to these drugs.

Drug Interactions

H2 receptor antagonists can interact with several drugs, including:

  • Antacids: May reduce the absorption of H2 receptor antagonists.
  • Warfarin: H2 receptor antagonists may increase the effects of warfarin, increasing the risk of bleeding.
  • Proton pump inhibitors: Concurrent use with H2 receptor antagonists may reduce the effectiveness of both drugs.

Always consult with a healthcare provider before starting or stopping any medication.


H2 receptor antagonists are a valuable tool in the management of conditions related to excess stomach acid. As with any medication, they should be used under the guidance of a healthcare provider to ensure their safe and effective use.

Disclaimer: This article is for informational purposes only and should not be taken as medical advice. Always consult with a healthcare professional before making any decisions related to medication or treatment.

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