31. Drugs used in the treatment of peptic ulcer

Last updated on June 24, 2019 at 21:30

Peptic ulcer

Peptic ulcers are mucosal breaks that penetrate the mucosa and may penetrate into the submucosa. They’re usually in the stomach or duodenum. Duodenal ulcers are mostly associated with too much acid while gastric ulcers are mostly associated with decreased protective factors.

Both types are associated with alcohol, NSAID use, stress and most importantly, helicobacter pylori. H. pylori is responsible for the vast majority of peptic ulcers. It’s diagnosed based on the urea breath test, where the patient ingests radioactively labelled urea. H. pylori has a urease enzyme which breaks down urea into ammonia and bicarbonate. Some of the bicarbonate is exhaled as CO2. The amount of radiolabelled CO2 can be measured.

The main symptom is pain. Duodenal ulcers usually cause pain when fasting which improves upon eating, while gastric ulcers cause pain that becomes worse when eating. Bleeding may also occur.

Peptic ulcers are treated conservatively with drugs. There are many types of drugs available to treat the disease. First we must look at the mechanisms of which acid is secreted and how the mucosa is protected from it.

The mechanisms that regulate gastric acid production.

The HCl component of stomach acid is produced by the H+/K+ ATPase, also called the proton pump, inside parietal cells. As you can see from the figure are there many factors that influence the activity of the proton pump. This means that there are also many possibilities for drugs to regulate gastric acid production.

Proton pump inhibitors

These drugs, often called PPIs, inhibit gastric acid production by the easiest mechanism: by binding to and inhibiting the proton pump itself. The prototype is omeprazole but other types exist like esomeprazole and lansoprazole.

Indications:

GERD, peptic ulcer, Zollinger-Ellison syndrome, acid reflux.

Mechanism of action:

PPIs bind to the H+/K+ ATPase and inhibit it irreversibly. These drugs are lipophilic weak bases that are inactive at neutral pH. Because they are lipophilic can they cross the cell membrane of parietal cells and enter them. The environment inside the parietal cells is highly acidic. This causes the PPIs to take up H+ from the environment and become protonated. They are now no longer lipophilic as they have a positive charge, so they are “trapped” inside the parietal cells.

Dosage:

These drugs are given orally inside enteric-coated granules that prevent them from being trapped inside the stomach. The drugs are released inside the intestines, where they are absorbed and travel with the blood to the parietal cells of the stomach. They should be taken in the morning.

Side effects:

They have few and rare side effects. Long-term usage is associated with osteoporosis and increased risk of gastrointestinal infections. Atrophic gastritis may occur in long-term use in people who are H. pylori positive.

Histamine 2 receptor antagonists

These drugs block the histamine 2 receptor which normally stimulates gastric acid secretion. The important ones are cimetidine, ranitidine and famotidine. These drugs not only decrease acid secretion but also pepsin secretion. They promote ulcer healing.

Indications:

GERD, peptic ulcer. Prophylaxis against stress ulcer.

Pharmacokinetics:

H2 receptor antagonists are eliminated by renal excretion.

Muscarinic antagonists

M1-selective muscarinic antagonists like pirenzepine and telenzepine block the neuronal regulation of gastric acid production. These drugs are only used for ulcers that don’t respond to PPI or H2 blocker therapy.

These drugs have parasympatholytic side-effects like bronchodilation and decreased secretions.

Other acid inhibitors

Octreotide is a somatostatin (SST) analogue which mimics the effects of somatostatin. One of these effects is to decrease HCl, pepsin and gastrin secretion. It’s used to decrease bleeding from ulcers or oesophageal varices in portal hypertension.

Antacids

Antacids are weak bases which forms salts with HCl in the stomach, neutralizing the acid. Most antacids that are used are salts of both magnesium and aluminium. Magnesium salts cause diarrhoea and aluminium salts cause constipation, but by combining them can we preserve normal bowel function.

Bicarbonate is rarely used as an antacid nowadays.

Indications:

Symptomatic treatment for GERD, heartburn.

Mechanism of action:

In the stomach will Al3+ and Cl form a salt that forms a protective layer on the mucosa. Aluminium binds phosphate in the intestines, which prevents phosphate from being absorbed.

Counterindications:

Usage of aluminum and magnesium-containing antacids in people with renal failure causes hyperaluminaemia and hypermagnesaemia.

Interactions:

Because they alter the pH may they decrease the absorption of drugs like digoxin, anticoagulants and antibiotics.

Side effects:

Bicarbonate forms CO2 when it meets the acid in the stomach, which may cause discomfort and flatulence.

It’s important to keep in mind that development of milk-alkali syndrome may occur in antacid administration. The syndrome develops when a person consumes too much calcium and alkali. All antacids are alkali, so people shouldn’t drink milk when using antacids.

Mucosal protectants

These drugs enhance endogenous mechanisms that protect the mucosa or they provide a physical protective barrier for the mucosa.

Sucralfate is a substance that creates a thick gel-like protective layer on the mucosa and especially on the ulcers. This drug needs acidic pH to work and should therefore not be used with acid-lowering drugs. It’s mostly used as a prophylactic of stress-induced ulcers.

Bismuth compounds are compounds with the ion bismuth (Bi3+). Bismuth has bactericide effect against H. pylori and forms a protective layer on the mucosal surface. May be used together with antibiotics against the bacterium. Very little bismuth is absorbed but like for aluminium can it cause encephalopathy in renal failure. Rarely used as they cause black discoloration of the teeth and tongue.

Misoprostol is a prostaglandin E1 analogue. Prostaglandin E1 has protective effects on the mucosa. It decreases acid secretion, increases mucous and HCO3 secretion and increases mucosal blood flow. It’s used to prevent NSAID-related ulcers in long-term NSAID therapy. Diarrhoea and nausea are very common side-effects.

Carbenoxolon is derived from the liquorice plant. It increases gastric mucus production and decreases acid production. It’s not frequently used due to its mineralocorticoid-like side-effects.

Antibacterial treatment

The go-to treatment of H. pylori-positive peptic ulcer, the so-called “classic treatment” consists of 7 days treatment with:

  • A proton pump inhibitor
  • Clarithromycin
  • Amoxicillin

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