Week 3: GI pharmacology

Question 1

vagus nerve stimulation and acid secretion

Answer 1

• stimulates G cells to produce gastrin
• D cell to inhibit somatostatin
• endochromaffin like cell to produce histamine
• parietal cell to produce acid

Question 2

Acid neutralization drugs

Answer 2

1. sodium bicarbonate
2. magnesium hydroxide (maalox and mylanta)
3. aluminum hydroxide - maalox and mylanta
4. calcium carbonate- Tums

Question 3

Side effects of acid neutralization drugs

Answer 3

• magnesium hydroxide causes diarrhea

- aluminum hydroxide results in constipation

Question 4

H2 receptor antagonists

Answer 4

-they block histamine receptor to decrease acid secretion. But acid production not completely shut down
Drugs
-Cimetidine
-Ranitidine
-Famotidine
-Nizatidine

Question 5

Side effects of H2 receptor antagonists

Answer 5

• primarily associated with cimetidine. Interferes with drug metabolism by reducing activity of cP450
• other drugs dosages have to be reduced
• cimetidine also binds to androgen receptors and aromatase enzymes and males may suffer erectile dysfunction and loss of libido, gynecomastia

Question 6

Proton pump inhibitors

Answer 6

-works at H/K ATPase. Orally administered have time release. Dissolve and absorbed in small intestines, travels through blood stream and concentrates in gastric pits
-PPI is activated when exposed to acid.
Drugs
-omeprazole
-esomeprazole
-lansoprazole
-pantoprazole

Question 7

Side effects of PPIs

Answer 7

• interfere with calcium pump which results in hypocalcemia and osteopenia (textbook)
• recent evidence shows that magnesium pump is inhibited and that results in hypocalcemia. Rx by giving Ca and Mg supplements
• Hypertrophic polyps due to increase in gastrin levels. G cell (not inhibited by somatostatin) and parietal cell both hypertrophy

Question 8

Drugs for mucosal protection

Answer 8

1. Sucralfate: activated by stomach acid. Binds to mucous layer and protects it. Don’t take with antacids, H2 receptor inhibitors, or PPI
2. Misoprostal: prostaglandin that stimulates mucus production by stomach mucosa

Question 9

Drugs that promote Gi motility

Answer 9

1. Metoclopramide: D2 receptor inhibitor. Acts by blocking sympathetic input or blocking D2 receptors on cholinergic neurons.
   -D2 receptors inhibits Ach release. blockade of them allows Ach release and increase in peristalsis.
   NOT USED
2. Neostigmine: cholinesterase inhibitor
3. Erythromycine: binds to motilin receptors

Question 10

Drugs for nausea and vomiting

Answer 10

1. Antihistamines
   -diphenylhydramine
2. Cholinergic antagonists> blocks vestibular input.
   -scopolamine
3. dopamine antagonist. blocks D2 receptors in chemo sensing center
   -Metoclopramide
4. 5HT3 receptor inhibitors
   -odansetron
   for chemotherapy induced
5. Augmenters of 5HT3: steroids, neurokinins, cannabinoids

Question 11

Drugs for constipation

Answer 11

1. lifestyle first
   - increase fiber, fluid, exercise, don’t delay
2. bulking laxatives-metamucil
3. irritant/stimulant laxatives: bisacodyl
4. osmotic laxatives: magnesium hydroxide, polyethylene glycol
5. chloride channel inhibitor: lubiprostone for constipating IBS
6. stool softeners: docusate
7. opioid antagonist

Question 12

Drugs for diarrhea

Answer 12

1. opioid angonist: block Ach release
   - diphenoxylate
   - loperamide (immodium)
2. somatostatin agonist
   - octreotide (for tumor induced)
3. water absorbing drugs-colloidal bismuth (peptic bismol)

Question 13

Drugs for IBS

Answer 13

1. for cramping and pain
   - cholinergic agonist: dicyclomine and hyoscyamine
2. constipation
3. diarrhea
   - 5HT3 receptor blocker: alosetron. blocks cholinergic input to colon, slows motility and allows time for water absorption