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This article will describe the most common medical conditions of gastrointestinal tract and the use of H2 receptor blockers.

1.Drugs used to treat peptic ulcer

2.Drugs used to treat chemotherapy-induced nausea and vomiting.

3.Drugs used to treat diarrhea and constipation.

1.Drugs used to treat peptic ulcer

The pathogenesis of peptic ulcer diseases is not exactly known.

However, 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

Treatment approaches to treat peptic ulcers

1. Eradicating the infection of h-pylori
2. To reduce gastric acid secretions
3. Preventing gastric mucosa damage

Drugs to treat peptic ulcer disease

1. Antimicrobial agents

These include

• 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

Mechanism of action of H2 receptor blockers:

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.

               Therapeutic uses of H2 receptor blockers:

1. Peptic ulcers

Both gastric and duodenal ulcers are treated with h2 receptor antagonists.

• Acute stress ulcers

These drugs are administered to patients with major trauma in intensive care unit managing acute stress ulcers linked with physical trauma.

• Gastroesophageal reflux diseases (Heart burn)

Low dose of h2 receptor antagonist can heal heart burn or Gastroesophageal reflux disease.

Although, tolerance to H2 antagonist can be seen within 2 weeks of therapy.

Pharmacokinetics of H2 receptor antagonist

1. Cimetidine
2. It is administered orally
3. Widely spread in the body
4. Excreted through urine
5. It has short half life
6. 30 of drug is metabolized in the liver and 70% is excreted through urine unchanged.
7. 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.

Adverse effects of H2 receptor antagonists:

the most common side effects of cimetidine are:

• headache
• dizziness
• diarrhea
• muscular pain
• confusion and hallucinations
• gynecomastia galactorrhea
• reduced sperm count
• inhibit first pass metabolism of alcohol.