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GASTROINTESTINAL DRUGS

 

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Drugs Used to Control Gastric Acidity and Secretion

The acidic nature of the gastric juices is essential for activating digestive protease activity and controlling intestinal bacteria. The gastric acids, however, can cause severe ulceration and hemorrhage of the stomach lining if excessive amounts of acid are produced or if the normal protection of the stomach mucosa is disturbed by irritants, drugs, or bacterial infection. Agents used to control gastric acidity and secretion are as follows;

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DETAILED MECHANISM OF ACTION OF PPI AND THERAPEUTIC USES

MECHANISM OF ACTION

The proton-pump inhibitors inhibit gastric acid by blocking the H+/K+-adenosine triphosphatase enzyme system (the proton pump) of the gastric parietal cell. PPIs undergo rapid first-pass and systemic hepatic metabolism and have negligible renal clearance

PPIs are administered as inactive prodrugs. To protect the acid labile prodrug from rapid destruction within the gastric lumen, oral products are formulated for delayed release as acid-resistant, enteric-coated capsules or tablets. After passing through the stomach into the alkaline intestinal lumen, the enteric coatings dissolve and the prodrug is absorbed. The PPIs are lipophilic weak bases (pKa 4–5) and, after intestinal absorption, diffuse readily across lipid membranes into acidified compartments (e.g., the parietal cell canaliculus). The prodrug rapidly becomes protonated within the canaliculus and is concentrated more than 1000-fold by Henderson-Hasselbalch trappin. There, it rapidly undergoes a molecular conversion to the active form, a reactive thiophilic sulfonamide cation, which forms a covalent disulfide bond with the H+ /K+ - ATPase, irreversibly inactivating the enzyme

THERAPEUTIC EFFECTS

gastroesophageal reflux disease

PPIs are the most effective agents for the treatment of erosive reflux disease, esophageal complications of reflux disease (peptic stricture or Barrett’s esophagus), and extra-esophageal manifestations of reflux disease.

PEPTIC ULCER DISEASE

PPIs afford more rapid symptom relief and faster ulcer healing for duodenal ulcers and, to a lesser extent, gastric ulcers. All the pump inhibitors heal more than 90% of duodenal ulcers within 4 weeks and a similar percentage of gastric ulcers within 6–8 weeks.

H-Pylori associated ulcers

Effective regimens for H pylori eradication are combinations of two antibiotics and a PPI. PPIs promote eradication of H pylori through several mechanisms:

  • direct antimicrobial properties (minor) and—by raising intragastric pH
  • lowering the minimal inhibitory concentrations of antibiotics against H pylori.

Triple therapy

the most commonly recommended treatment regimen consisted of a 14-day regimen of “triple therapy

  • PPI twice daily
  • clarithromycin, 500 mg twice daily
  • either amoxicillin, 1 g twice daily, or metronidazole, 500 mg twice daily.

NSAID ASSOCIATED ULCER

—For patients with ulcers caused by aspirin or other NSAIDs, following is prescribed

  • H2 antagonists
  • PPIs
  • NSAID is discontinued

PREVENTION OF REBLEEDING FROM PEPTIC ULCER

In patients with acute gastrointestinal bleeding due to peptic ulcers, the risk of rebreeding from ulcers that have a visible vessel or adherent clot is increased.

Drugs administered are;

PPIs (high-dose oral therapy, or as a continuous intravenous infusion.)

NON ULCER DYSPLASIA

PPIs have modest efficacy for treatment of non-ulcer dyspepsia, benefiting 10–20% more patient

PREVENTION OF STRESS RELATED MUCOSAL BLEEDING

The agents used to relieve the symptoms are;

  • H2 receptor agonist
  • PPIs (omeprazole)

GASTRINOMA AND OTHER HYPERSECRETORY CONDITIONS

In patients with metastatic or unrespectable gastrinomas, massive acid hypersecretion results in peptic ulceration, erosive esophagitis, and malabsorption. With PPIs, (omeprazole) excellent acid suppression can be achieved in all patients

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