Gastrointestinal Ulcers Flashcards
What produces the acid in the stomach?
Parietal cells
Kill bacteria, viruses and other parasites, not for digestion
What is an example of a systemic antacid? How does it work?
NaHCO3
Dissociates into Na and HCO3 (bicarbonate)
The bicarbonate ion is absorbed into the blood and slightly increases pH (alkalosis) and elevates pH of the stomach, short term
What are the problems with NaHCO3?
Alkalotic urine can increase the deposition of calcium and phosphate to form a kidney stone (cranberry opposes) this increases blood Na, exacerbating hypertension
Acid rebound due to feedback regulation (take with acidic drink/food)
What are some examples of non-systemic antacids? How do they work?
CaCO3, Al(OH)3, Mg(OH)2
Do not affect extracellular or blood pH
Short term
What are the problems with aluminum and calcium antagcids?
Cause constipation so they are often combined with magnesium
How are anticholinergics used in gastric ulcers?
Inhibit the muscarinic Ach receptors in parietal cells which stimulate HCl secretion
Acid secretion is not reduced by much (40%) and there are many side effects (dry mouth, vision, sedation)
What is sucralfate?
An aluminum base salt that binds to hydrogen ions to form a gooey paste, increasing pH and also binds to degenerating cells, forming a protective layer
Not absorbed into bloodstream but can inhibit absorption of other drugs
Works for 8-12 hours
How does misoprostol work?
A prostaglandin analogue that stimulates production of the mucosal barrier
Only works locally
How do histamine H2 blockers work?
Inhibits H2 receptors, which normally increase HCl production
What are some examples of H2 blockers?
Cimetidine (binding to CYP450 causes drug interactions, binds to androgen receptors giving gynecomastia, recduced libido, impotence)
Ranitidine (more effective, less drug interaction, does not bind androgen receptors)
Famotidine (most effective, best safety profile, more effective at high pH so given with antacid)
How do proton pump inhibitors work?
Inhibits gastric H/K ATPase (proton pump), binds to H extrusion sites and block the release of H and Cl
They enter the secretory canaliculus of the parietal cell which opens when acid secretion occurs (prodrug converted to active drug here), bind very tightly, giving long half life
What are some examples of proton pump inhibitors?
Omeprazole (prilosec)
Esomeprazole (nexium), lansoprazole, pantoprazole, rabeprazole (also increases mucous secretion)
How does H.Pylori infection cause an ulcer?
Burrows into gastric mucosa to escape gastric acid, it then produces urease, which converts urea to ammonia and CO2 which kills mucosal epithelial cells (lots of belching)
Not all patients with an ulcer has an H.pylori infection
How do we test for an H.pylori infection?
Breath test for urea, serological, culture, histology, stool sample
How is an H. pylori infection treated?
Triple therapy: A PPI to control acid and 2 effective antibiotics to kill the HP
Quadruple: Add bismuth
Most effective treatments for ulcers caused by HP, long course of therapy because difficult to reach area
