Drugs to treat disorder of gastric acid secretion Flashcards
What is an antacid?
An antacid is any substance, generally a base, which counteracts stomach acidity.
They act by buffering gastric acid, thereby raising the gastric pH.
e.g.: Aluminum hydroxide and magnesium hydroxide (Maalox®)
Calcium carbonate and magnesium carbonate (Rennie®)
What is an alginate?
Anionic polysaccharides that form a viscous gel upon binding water.
Often combined with antacids for use in reflux oesophagitis.
Increase the viscosity of stomach contents and can protect the oesophageal mucosa from acid reflux.
The viscous gel (‘raft’) floats on the surface of the stomach contents, thereby reducing symptoms of reflux.
e.g. sodium alginate, sodium bicarbonate, calcium carbonate Gaviscon®
What are histamine H2-receptor antagonists?
Competitively inhibit histamine actions at H2-receptors.
Decrease basal and stimulated acid secretion.
e.g. ranitidine Zantac®
What do proton pump inhibitors do?
Irreversibly inhibit the H+/K+-ATPase pump, the terminal step in the acid secretory pathway.
Decrease both basal and stimulated acid secretion.
Are more effective than H2-receptor antagonists.
Are inactive at neutral pH.
Accumulate in secretory canaliculi of parietal cells and are activated in acid environment. therefore very specific.
e.g. Omeprazole Losec®, Prilosec®, Zegerid®
Lansoprazole Prevacid®, Zoton®, Inhibitol®
What are the conditions requiring drug treatment of acid secretion?
1) reflux oesophagitis
2) peptic ulcer
- non-steroidal anti-inflammatory drugs (NSAIDS)
- Zollinger-Ellison Syndrome
- H. Pylori infection
What are the symptoms and complications of reflux oesophagits?
Symptoms: Heartburn Regurgitation Haematemesis – vomiting of blood caused by irritation of gastric lining Complications: Oesophageal ulceration Peptic stricture – in elderly, narrowing of oesophagus Barrett’s oesophagus
How do prostaglandins renew the gastric mucosal barrier?
Prostaglandins E2 and I2 simulate and support renewal of the gastric mucosal barrier by:
1) stimulating gastric mucus production
2) stimulating bicarbonate secretion
3) inhibiting gastric acid production
4) promoting local healing
What is Zollinger-Ellison syndrome?
Increased levels of the gastrin are produced. (Gastrin causes parietal cells to secrete HCl)
Often, the cause is a gastrin-producing tumour (gastrinoma) of the duodenum or pancreas. Ectopic tumour.
Gastrin increases acid secretion, which can lead to peptic ulcers (95% of patients).
Gastrin also acts as a trophic factor for parietal cells, causing parietal cell hyperplasia.
Therefore there is an increase in the number of acid secreting cells, with each producing acid at a higher rate.
What is the treatment for Zollinger-Ellison syndrome?
Proton pump inhibitors and H2-receptor antagonists are used to slow down acid secretion.
Tumours are removed surgically (if possible) or treated with chemotherapy.
What does Helicobacter Pylori do?
A spiral-shaped Gram-negative bacterium, which damages stomach and duodenal tissue.
Produces and secretes urease, which breaks down urea into CO2 and NH3.
NH3 neutralises gastric acid.
H. pylori penetrates mucus barrier, facilitating acid penetration.
NH3, other bacterial products, and acid damage epithelial cells.
What is the treatment for H. pylori infection?
Eradication regimens include antibiotics (to get rid of H Pylori) and a proton pump inhibitor (to suppress acid secretion to make H pylori less effective at damaging mucosal membrane).
Eradication of H. pylori can produce long-term remission of ulcers.
What are the causes of under-secretion of gastric acid?
Achlorhydria (absence of gastric acid)/ Hypochlorhydria (reduction of gastric acid): absence / deficiency of hydrochloric acid in gastric juice, e.g.
- iatrogenic
- atrophy of gastric mucosa (older adults)
What are the consequences of under-secretion of gastric acid?
impaired ability to digest and absorb certain nutrients, such as iron, and the B vitamins.
increased vulnerability of GI tract to bacterial infection.
