GI Drugs I and II Flashcards
What is the stomach cell type that secretes acid? What are the 3 stimulants of acid secretion?
Parietal cells
Ach
gastrin
histamine
What are the 3 major stimuli for acid secretion and their receptors?
Ach - M3 receptors
gastrin - CCK2 receptors
histamine - H2 receptors
What are the two secretions of the stomach epithelia?
Mucus
Bicarbonate
An important step in the formation of stomach acid is H2CO3 formation. What is the enzyme responsible?
Carbonic anhydrase
What are the 3 ion transporters involved in gastric acid secretion?
H+ / K+ antiporter
K+ Cl- symporter
HCO3 / Cl antiporter
Of the 3 major stimulants for the secretion of gastric acid, which are Ca++ dependent and which are cAMP dependent?
Gastrin and Ach - Ca++ dependent
Histamine - cAMP
Regarding cephalic stimulated acid response, what nerve is involved and what and where is the target cell?
Vagus nerve
Enterochromaffin cell in stomach fundus
What is the neurotransmitter used by enterochrommafin like cells to stmulate acid secretion from parietal cells? What is the target receptor on the parietal cells? This release is [ fast and short / slow and prolonged ]?
Histamine
H2 receptors
Slow and prolonged
Slow and prolonged release of acid from parietal cells is produced by stimulation of _ receptor. Rapid release of acid is produced by stimulation of _ receptor. What is the stimulus for the rapid response?
H2
M3
Vagus nerve Ach
In addition to the vagus nerve stimulating enterochrommafin like cells to produce acid, what cell type can also stimulate enterochrommafin like cells? What is their target receptor? Where are they located?
G cells
CCK2 receptor
Antrum of stomach
Prostaglandins are [protective / non-protective] of the intestinal mucosa. What is the mechanism (2)?
Protective
- Activate Gi GPCRs to inhibit cAMP to decrease acid
- Increase secretion of mucus and bicarbonate
If prostaglandins downregulate the cAMP dependent acid production, which of the 3 main stimulants of acid secretion is affected by this? (histamine, gastrin, acetylcholine)
Histamine - H2 receptor effects is cAMP dependent
What are the 3 examples of proton pump inhibitors provided? What is their mechanism?
Omeprazole, esomeprazole and lansoprazole
Covalently bind and irreversibly inhibit H+/K+ ATPase
Proton pump inhibitors are the first line treatment for hyperacidity and ulcers. If they only work for 2 hours, why are they only used 2 times a day?
Because of slow turnover of the H+/K+ ATPase at apical surface
What is the acid requirement for proton pump inhibitors?
All PPIs are prodrugs, require acid to be activated inot their active forms
How do proton pump inhibitors reach their targets in the parietal cells?
- Absorbed as high pH form into blood
- Enter parietal cell and is activated / trapped
GERD, erosive esophagitis, peptic ulcers and NSAID induced gastric ulcers can all be treated with _
proton pump inhibitors
What is Zollinger - Ellison syndrome? How is it treated?
Gastrin secreting tumor from pancreas or intestine
proton pump inhibitor
What is the percentage of acid that can be reduced using proton pump inhibitors? Why does the treatment require 2-5 days to work?
Up to 90% reduction in stomach acid
Only active proton pumps (small percentage) react with PPIs
How are PPIs cleared from circulation?
Through the liver
How does hepatic failure affect PPIs?
Reduced clearance of the PPIs
Serum concentration of what drug is increased following PPI use? Activation of what drug is decreased?
Warfarin serum concentrations increased
Reduced activation of clopidogrel
What can happen with suddenly stopping the use to PPIs?
Rebound hypergastrinemia and gastritis
Which is more powerful in reducing acid secretion, H2 antagonists or PPIs? What cell is the source of the histamine antagonized by H2 receptor blockers?
PPIs (90%), H2 blockers (70%) reduction
enterochrommafin like cells
How are H2 receptor blockers excreted?
renal organic cation system
What are the 3 examples of H2 receptor antagonists provided? What are their durations of action?
Cimetidine 4-5 hrs
Ranitidine 6-8 hrs
Famotidine 10 - 12 hrs
What is the effect of long term use on testosterone? On estradiol? 3 effects in men?
Reduced testosterone binding to receptor Hydroxylation of estradiol in women (galactorrhea) -reduced sperm count -impotence -gynecomastia
What is the effect of H2 blockers on pepsin and intrinsic factor? How long till tolerance occurs?
Reduced pepsin and IF
3 days
What is misoprostol? What is it used for? What 2 agents are preferred to misoprotol for this use?
Synthetic analog of PGE1
Used to prevent NSAID induced injury
PPIs and H2 antagonists
What 2 populations should not use misoprostol?
Inflammatory bowel disease patients Pregnant patients (can increase uterine contractions)
What is sucralfate? How does it work?
An octasulfate of sucrose
Forms sticky polymer coating that swells and covers epithelium at neutral pH
What is the use of sucralfate? What types of drugs should be avoided when using sucralfate? Why?
Stress ulcers
PPIs, H2 blockers - activated by acid
What is the main side effect of sucralfate? What is its effect on absorption?
Constipation
Can reduce absorption of other drugs
How do antacids work? What are the 3 examples provided?
Simple neutralize stomach acid
Aluminum hydroxide
Magnesium hydroxide
Calcium carbonate
What is the difference between aluminum and magnesium hydroxide?
Al - Slower acting, delays gastric emptying
Mg - faster acting, enhances motility
What drug interaction is likely with aluminum hydroxide?
Binds up tetracyclines