123 - Antiemetic, Antidiarrhoeal Drugs

Question 1

Example of a D2 antagonist

Answer 1

Metaclopramide

Question 2

Metaclopramide effects

Answer 2

Increases contractions in upper GIT, which makes stomach empty more quickly.

5HT4 receptor stimulation -> ACh release (Metaclopramide).

Metaclopramide also has dopaminergic effects. Blocks dopamine in the gut.

D2 antagonist

Question 3

Is metaclopramide a reversible or irreversible antagonist?

Answer 3

Reversible.
If taken long-term, D2 antagonists can have permanent effects (severe side effects - extrapyramidal side-effects - uncontrollable muscle movements of your lips, tongue, eyes, face, arms, or legs)

Question 4

Example of a 5HT3 antagoinst

Answer 4

Ondansetron

Question 5

Ondansetron side effects

Answer 5

Constipation.

Headaches.

Question 6

What are metaclopramide and ondansetron used to treat?

Answer 6

Nausea, vomiting

Question 7

Endogenous compound that stimulates NK1 receptors

Answer 7

Substance P

Question 8

Example of a neurokinin-1 receptor antagonist

Answer 8

Aprepitant

Question 9

How is aprepitant administered?

Answer 9

Always in combination with another drug

Question 10

Example of two add-on drugs for nausea, emesis

Answer 10

1) Aprepitant

2) Dexamethasone (glucocorticoid)

Question 11

What are neurokinin-1 receptor antagonists used for?

Answer 11

Anti-emetic

Question 12

Bulking agents

Answer 12

Hydrophilic colloids.
Indigestible vegetable fibre that increases faecal water retention, therefore increasing volume of faeces.
Increases normal reflex bowel activity.

Question 13

Examples of bulking agents

Answer 13

Bran, Psyllium, Ispaghula husk, Sterculia.

Psyllium is the most important to remember

Question 14

Side effects of bulking agents

Answer 14

Water loss.
If constipation is slow-transit, or is opioid-induced, can just contribute to faecal mass, increase impaction.
Increased flatulence.

Question 15

Does chronic use of stimulant laxatives cause an atonic colon?

Answer 15

Maybe causes permanent atonia of colon, but it is not clear

Question 16

Four groups of laxatives 
1
2
3
4

Answer 16

1) Bulking agents
2) Faecal softeners and lubricants
3) Osmotic laxatives
4) Stimulant laxatives

Question 17

Example of a faecal softener and lubricant

Answer 17

Docusate.

Question 18

Docusate
1
2
3

Answer 18

Faecal softener and lubricant.
Frequently prescribed for people on opioids.
A detergent, so increases mixture of water into faeces.

Question 19

Danger of using paraffin wax for constipation

Answer 19

Can adsorb fat-soluble vitamins.

Can be accidentally inhaled, cause issues in the lungs.

Question 20

Types of osmotic laxatives
1
2
3
4

Answer 20

1) Saline laxatives
2) Disaccharide hydrophilic colloid
3) Polyols
4) Macrogols or polyethylene glycols

Question 21

Example of an osmotic laxative

Answer 21

Magnesium salts (a saline laxative)

Question 22

How do disaccharide (galacto-fructose) hydrophilic colloids work?

Answer 22

Draw water into faeces through osmosis

Question 23

Which laxative is included in some confectionary as an artificial sweetener?

Answer 23

Polyols

Question 24

Most-potent laxatives

Answer 24

Stimulant laxatives

Question 25

How do stimulant laxatives work?

Answer 25

Precise mode of action is not known but may stimulate colonic myenteric nerve plexuses,
irritate intestinal mucosa or by direct sensory nerve ending irritation → increase motility.
May also reduce net reabsorption of water and electrolytes.

Question 26

Example of a stimulant laxative

Answer 26

Senna

Question 27

Another name for stimulant laxative

Answer 27

Irritant laxative

Question 28

Types of antidiarrhoeal drugs
1
2
3

Answer 28

1) Opioids
2) Musculotropic antispasmodic
3) Muscarinic R antagonists

Question 29

Example of an opioid used to reduce diarrhoea

Answer 29

Loperamide

Question 30

How do opioid antidiarrhoeals work (basically)

Answer 30

Antagonise mu opioid receptors, blocking ACh release.

Question 31

Why doesn’t loperamide cause the CNS effects of other opioids?

Answer 31

Doesn’t cross blood brain barrier

Question 32

Musculotropic antispasmodic

Answer 32

Mebeverine

Question 33

Example of a muscarinic R antagonist

Answer 33

Hyoscine butylbromide

Question 34

Anti-flatulence drug

Answer 34

Simethicone

Question 35

Simethicone effect

Answer 35

Defoaming polymer, that changes surface tension of small gas bubbles, allowing them to join into larger gas bubbles which can be passed more easily.