Block 15

Question 1

Mechanism of Ranitidine

Answer 1

Histamine (H2) Receptor antagonist
- selectively, reversibly and competitively block H2 histamine receptors on parietal cells membranes

• inhibits basal + stimulated gastric acid secretion

Question 2

Which type of drugs can be used for acute relief of heartburn symptoms?

Answer 2

Histamine (H2) receptor antagonists –> more rapid onset of action than PPIs

Question 3

Mechanism of PPI (proton pump inhibitors)

Answer 3

bind covalently and irreversibly to inhibit H+/K+-ATPase in gastric parietal cell

reduces basal + stimulated acid secretion

Question 4

How are PPIs are administered?

Answer 4

PPIs are administered as inactive prodrugs + accumulate in canaliculus of parietal cells before being protonated + converted to active form

Question 5

What are antacids?

Answer 5

weak bases that buffer or neutralise gastric HCL to form a salt + water, reducing gastric acidity

Question 6

Give 2 examples of systemic antacids

Answer 6

• Sodium bicarbonate

- Calcium carbonate

Question 7

Sucralfate

Answer 7

mucosal protective agent

provides a physical barrier over the surface of a gastric ulcer + enhances the gastric mucosal protective system

Question 8

Misoprostol

Answer 8

synthetic prostaglandin E1 analogue

helps create alkaline mucus layer + inhibits gastric acid secretion

Question 9

Give an example of an Adsorbent and how it acts

Answer 9

Bismuth subsalicylate

• absorbs bacterial toxins + fluid in the gut

Question 10

Loperamide MoA

Answer 10

non-selective Ca2+ channel blocker AND binds to opioid muRs in myenteric plexus of lrg intestine

==> SLOWS intestinal motility

Question 11

Give 2 examples of antispasmodics

Answer 11

Mebeverine

Scopolamine - competitive antagonist at muscarinic Rs

Question 12

Which agents help to rebalance fluid + electrolytes lost during a diarrhoeal episode?

Answer 12

Oral rehydration agents

Question 13

Give an example of an NK1 antagonist

Answer 13

Aprepitant

Question 14

Aprepitant MoA

Answer 14

NK1Antagonist

• blocks action of neurokinin-1 (substance p) in the brain

Question 15

Diphenhydramine MoA

Answer 15

block vestibular system input into chemoreceptor trigger zone

Question 16

MoA of Dopamine antagonists

Answer 16

block D2 dopamine receptors in medullary chemoreceptor trigger zone prevent vomiting e.g. Metoclopramide

Question 17

Ondansetron MoA

Answer 17

serotonin R antagonist:

block 5-HT3 receptors in the CNS and GI tract.

Activation of these receptors normally triggers vomiting

Question 18

Bulk forming laxatives

Answer 18

• improve stool formation by adding bulk to the diet
• are insoluble + nonabsorable from the intestine
• absorb + retain water which softens + hydrates faecal material

Question 19

Give an example of a faecal softener and explain how they act

Answer 19

Example: Docusate

softens stools by decreasing surface tension + increasing water/intestinal fluid penetration into stools

Question 20

MoA of Osmotic Laxatives

Answer 20

• increase water in the large intestine to soften the stool and promote bowel movement
• stretching of bowel lumen due to increased water stimulates peristalsis

Examples: Magneisum Hydroxide