Pharm of Acid-Peptic Disorders Flashcards
What is the most common cause of peptic ulcers?
H. pylori infection.
What is the 2nd most common cause of peptic ulcers?
Medication-induced (NSAIDs).
What is the role of gastric acid? What cells produce it?
Digestion of proteins
Activates pepsinogen to pepsin, which activates the other digestive enzymes
Absorption of calcium, iron, B12
Suppresses bacterial growth
Cephalic Phase of Gastric Acid Secretion
Vagus nerve mediated. ACh is the NT. It binds to muscarinic receptors on parietal cells due to the taste, thought, smell, sight, and swallowing of food.
Gastric Phase of Gastric Acid Secretion
Occurs due to the release of gastrin from G cells and binding to parietal cells to produce gastric acid in response to food or distention of the stomach.
What cells produce gastric acid?
Parietal cells.
Cl- exits the cell.
H+ exits via the K+/H+ pump.
HCO3- enters the blood via HCO3-/Cl- pump and is released by the pancreas to neutralize chyme in the duodenum.
What stimulates production of HCl from parietal cells?
Gastrin, Histamine, ACh.
What are the products of parietal cells?
HCl & intrinsic factor (for absorption of B12).
Acetylcholine
Major neural stimulator of parietal cells.
Increases gastrin release, stimulates parietal cells, stimulates enterochromaffin cells (Histamine-producing), and inhibits somatostatin.
Gastrin
The major endocrine regulator of HCl release from parietal cells.
Released from G cells in the gastric antrum in response to protein in meal, gastric distention.
Triggers HCl production. Also binds to EC cells and triggers release of histamine.
Histamine
Major autocrine/paracrine stimulator of parietal cells. H2 utilizes Gs coupled adendyly cyclase and cAMP to stimulate HCl secretion.
Somatostatin
Produced by S cells of the duodenum in response to gastric acid in the duodenum. Inhibits parietal cells by Gs coupled receptors and decreasing cAMP.
Prostaglandins
Autocrine factors secreted by macrophages and enothelial cells to inhibit acid secretion by decreasing cAMP.
Stimulates secretion of mucin and bicarb.
Inhibited by NSAIDs.
Pepsin
Zymogen activated by HCl. Activates the other digestive enzymes.
Becomes inactivated at pH >4.
What are the defensive mechanisms the gastric mucosa has against ulceration?
Mucin layer Lumenal Bicarbonate Somatostatin (< HCl production) Prostaglandins (< HCl production) Blood flow provides substrates/removes toxins
What must you consider when treating gastric ulcers?
What is the underlying cause?
If H. pylori, get rid of bacteria!
If medications, stop taking them! (NSAIDs).
Stop alcohol/smoking.
What is the main goal of treatment of gastric ulcers?
Decrease acid production.
What class of drugs is the most effective suppressor of gastric acid secretion and thus the DOC for treating gastric ulcers?
Proton pump inhibitors.
MOA: Act directly on the H+/K+ pump to prevent the production of acid from parietal cells of the stomach. Irreversible.
Multiple doses are necessary to inactivate all proton pumps.
Pro-drugs activated by food.
Most effective when parietal cell is stimulated post-prandially; because the amount of H+/K+ pumps is greatest after a prolonged fast, best to take it 20-30 minutes BEFORE eating breakfast.
PPIs: Examples
Esomeprazole, Lansoprazole, Omeprazole
-zole
Pharmacokinetics of PPIs
Rapidly absorbed.
Highly protein bound.
Extensively metabolized in the liver by P450.
Mostly excreted by the kidneys.
When should PPIs be taken?
20-30 minutes before breakfast since food will stimulate acid production after an overnight fast.
If 2x/day, take again 20-30 minutes before last meal.
Indications for PPIs
Peptic Ulcer Disease GERD Esophagitis Barrett's esophagus H. pylori ulcers (w/ antibiotic) NSAID-induced ulcers Stress ulcer prophylaxis Zollinger-Ellison Syndrome (cancer of gastrin-producing G cells)
Adverse Effects of PPIs
Nausea, abdominal pain, constipation/diarrhrea, flatulence, INCREASED GASTRIN LEVEL led to hyperplasia of enterochromaffin cells (Histamine-producing) leads to rebound hypersecretion of HCl once PPI is discontinued
A patient presents with NSAID-related gastric ulcers, but he is on Clopidogrel. What is of concern when giving PPIs? Which is safe for this patient?
PPIs may inhibit CYP2C19, which decreases metabolism and clopidogrel’s anti-platelet effect.
Dexlansoprazole is the only one approved for use with clopidogrel.