H2 Receptor Blockers Information

May 22, 2025 pharmacistsite

H2 Receptor Blockers antagonists, also known as H2 blockers, are medications that reduce stomach acid production by blocking the action of histamine on parietal cells in the stomach. They are used to treat a variety of acid-related gastrointestinal conditions, including ulcers, GERD, and heartburn. Common H2 blockers include cimetidine, ranitidine, famotidine, and nizatidine.

Medical Conditions of Gastrointestinal tract and the use of H2 receptor blockers.

Drugs used to treat peptic ulcer
Drugs used to treat chemotherapy-induced nausea and vomiting.
Drugs used to treat diarrhea and constipation.
Drugs used to treat peptic ulcer

The pathogenesis of peptic ulcer diseases is not exactly known.

major causes are:

Non-steroidal anti-inflammatory drugs NSAIDS
Infection of gram-negative H-pylori
More hydrochloric acid secretions
Less mucosal defense against gastric acid

Table of Contents

Treatment approaches to treat peptic ulcers

Eradicating the infection of h-pylori
To reduce gastric acid secretions
Preventing gastric mucosa damage

Drugs to treat peptic ulcer disease

These included:

Amoxicillin
Clarithromycin
Metronidazole
Tetracycline
Bismuth compounds

Patients infected with H-Pylori require antimicrobial therapy. As a result, Eradication of H pylori result in healing of ulcers. Also, it is possible by administration of combination of antimicrobial agents.

Triple therapy

PPI with either metronidazole or amoxicillin plus clarithromycin

Quadruple therapy

Bismuth subsalicylate and metronidazole plus tetracycline plus PPI.

These therapies are administered for 2 weeks.

H2 Histamine receptor blockers

H2 receptor blockers include

Cimetidine
Famotidine
Nizatidine
Ranitidine

H2 Receptor Blockers Mechanism Of Action

There action is on the H2 receptors selectively in stomach, blood vessels, and other sites. Moreover, they are competitive antagonists of histamine and are reversible. As a result, they inhibit secretion of histamine and gastrin.

H2 receptors:

Located on the basolateral surface of parietal cells, which are responsible for producing hydrochloric acid (HCl) in the stomach.

Histamine’s role:

Normally, after a meal, gastrin stimulates the release of histamine from enterochromaffin-like cells. This histamine then binds to H2 receptors on parietal cells, triggering the production of acid.

H2 blockers’ action:

H2 receptor antagonists competitively inhibit the binding of histamine to its receptor, thus reducing the stimulation of acid production.

Reduced acid secretion:

This leads to a decrease in the amount of acid secreted into the stomach, which can help heal ulcers and reduce symptoms of acid reflux and other related conditions.

Pharmacokinetics of H2 receptor antagonist

Cimetidine
It is administered orally
Widely spread in the body
Excreted through urine
It has short half life
30 of drug is metabolized in the liver and 70% is excreted through urine unchanged.
It inhibits cytochrome P450 and can interact with many other drugs resulting in severe side effects.

Ranitidine

It is 5 t0 10 folds more potent to cimetidine and is long-acting drug.
It has minimal side effects and does not result in antiadrenergic or practice stimulating effects
Additionally, it does not inhibit mixed function oxygenase system.

Famotidine

It is similar to ranitidine I pharmacological action
20 to 50 times more potent to cimetidine
3 to 20 times more potent than ranitidine.

Nizatidine

Nizatidine is similar to ranitidine in action and potency.
It is eliminated principally by kidney.
Its bioavailability is 100%.
Intravenous preparations are not available.

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