S10.2 Antiemetics And Antidiarrhoeals

Question 1

What causes us to vomit?

Answer 1

The chemoreceptor trigger zone stimulates the vomiting centre in the medulla signalling us to vomit.

Question 2

What can trigger the CTZ?

Answer 2

Sensory afferents (e.g bad smell).
Vestibular nuclei (e.g motion sickness).
Visceral afferents from gut (e.g bowel obstruction).
Direct triggers (e.g hormones – hyperemesis gravidarum, drugs – chemo, opiates).

Question 3

What is the mechanism of Muscarinic receptor antagonists?

Answer 3

E.g Hyoscine hydrobromide

Blocks muscarinic ACh receptors at vestibular nuclei and CTZ

Question 4

What are the uses and ADRs of Muscarinic receptor antagonists

Answer 4

Uses: motion sickness
ADRs: sedation, memory problems

Question 5

What is the mechanism of H1 receptor antagonists?

Answer 5

E.g cyclizine, promethazine

Inhibits histaminergic signals from the vestibular system to the CTZ in medulla

Question 6

What are the uses and ADRs of H1 receptor antagonists?

Answer 6

Uses: motion or morning sickness
ADRs: sedation, dry mouth

Question 7

What is the mechanism of 5HT3 receptor antagonists?

Answer 7

E.g ondansetron

Inhibits serotonin so reduces GI motility and secretions

Question 8

What are the ADRs of 5HT3 receptor antagonists?

Answer 8

Constipation, headache

Question 9

What is the mechanism of metacloperamide?

Answer 9

Increases ACh at muscarinic receptors in the gut. This promotes gastric emptying

Question 10

What are the uses and ADRs of metacloperamide?

Answer 10

Uses: GORD, IBS
ADRs: galactorrhoea

Question 11

What is the mechanism of domperidone?

Answer 11

Increases ACh at muscarinic receptors in the gut. This promotes gastric emptying

Question 12

What are the uses and ADRs of domperidone?

Answer 12

Uses: improves lactation
ADRs: cardiac death

Question 13

Which D2 RA act directly on the CTZ and what are their ADRs?

Answer 13

Chlorpromazine for motion sickness (Prochlorperazine in pregnancy).
Haloperidol for chemotherapy.
ADRs: parkinsonism, hypotension

Question 14

What are the uses and ADRs of corticosteroids?

Answer 14

E.g dexamethasone
Uses: perioperative vomiting, chemotherapy
ADRs: insomnia, hyperglycaemia

Question 15

What are the uses and ADRs of cannabinoids?

Answer 15

E.g nabilone
Uses: chemotherapy
ADRs: dizziness

Question 16

What is the mechanism of Neurokinin-1 RA?

Answer 16

E.g aprepitant

Inhibits substance P at CTZ

Question 17

What are the uses and ADRs of Neurokinin-1 RA?

Answer 17

Uses: chemotherapy
ARDs: headache, diarrhoea

Question 18

What 4 drugs do we prescribe for a patient with bowel problems?

Answer 18

Ondansetron + cyclizine, then add dexamethasone + metacloperamide.

Question 19

What is Hyperemesis Gravidarum and what do we prescribe for it?

Answer 19

During pregnancy, rapid rise in ẞhcg stimulates the CTZ.

Prescribe promethazine then metacloperamide + ondansetron.

Question 20

What is the mechanism and ADRs of opioid receptor antagonists for diarrhoea treatment?

Answer 20

E.g loperamide, codeine, morphine
Act on mu receptors so decrease the tone of smooth muscle and reduce peristalsis.
ADRs: paralytic ileus, vomiting

Question 21

Name some osmotic laxatives

Answer 21

E.g lactulose, macrogol

Help draw in or retain fluid

Question 22

Name some stimulant laxatives

Answer 22

E.g bisacodyl, senna

Increase intestinal motility

Question 23

Name a Bulk-forming laxatives

Answer 23

Methylcellulose

Question 24

Name a stool softener

Answer 24

Arachis oil