Nausea and Vomiting NOTFINISH

Question 1

What are the 5 main causes of nausea and vomiting?

Answer 1

• Gastrointestinal
• Chemical irritation
• Vestibular
• CNS
• Prengnacy

Question 2

Give an example for chemical irritation based cause of nausea and vomiting

Answer 2

Radiotherapy, drugs and toxins

Question 3

Give an example for a CNS based cause of nausea and vomiting

Answer 3

Anxiety, raised intracranial pressure

Question 4

What are the four sources of afferent input for the vomiting centre

Answer 4

1. Chemoreceptor trigger zone (CTZ)
2. Vestibular system
3. Vagal and spinal nerves from GI tract
4. CNS

Question 5

What triggers the chemoreceptor trigger zone to send signals to the vomiting centre?

Answer 5

Stimuli from the blood or CSF - e.g. drugs or toxins

Question 6

What triggers the vestibular system to send signals to the vomiting centre?

Answer 6

Motion sickness

Muscarinic and histamine receptor activation

Question 7

What triggers the vagal and spinal nerves of the GI tract to send signals to the vomiting centre?

Answer 7

Irritation of the mucosa causes release of serotonin by enterochromaffin cells.

5-HT3 receptors send signals.

Question 8

What do enterochromaffin cells release?

Answer 8

They release serotonin on irritation to the gut mucosa.

Question 9

What is the action of metoclopramide?

Answer 9

Enhances response to acetylcholine in GI tract

• Slows down peristalsis

Blocks dopamine receptors in CTZ

• Preventing vomiting reflex

Question 10

What are the side effects of dopamine blockers?

Answer 10

Extrapyramidal symptoms (movement-based effects)

Also, those that do cross the BBB cannot be used in Parkinson’s

Question 11

What type of drug CANNOT be used in patients with Parkinson’s Disease?

Answer 11

Dopamine blockers.

(Unless they do not cross the BBB - Domperidone)

Question 12

What are the three dopamine antagonists used in nausea and vomiting management?

Answer 12

Metoclopramide

Prochlorperzaine

Domperidone

Question 13

What is the action of prochlorperazine?

Answer 13

Anti-emetic effects due to dopamine antagonism (blocks CTZ vom reflex) and muscarinic receptor antagonism (slows peristalsis)

Question 14

What is the action of domperidone?

Answer 14

Dopamine antagonist that DOESNT cross teh BBB.

Blocks dopamine receptors in upper GI tract, resulting in increased motility

Orally administered, and safe to use in Parkinsons.

Question 15

How are 5HT3 antagonists named, giving two examples

Answer 15

Name ends in -setron

E.g. Ondansetron, Palonosetron

Question 16

What is the major and minor effect of 5HT3 antagonists?

For what causes of vomiting are they useful / not useful?

Answer 16

Major effect = block serotonin in upper GI tract

Minor effect = block vomiting centre and CTZ

5HT3 antagonists are most useful for causes mediated through irritation of the GI tract (major effect), not at all useful for nausea caused by other mechanisms, such as motion sickness through vestibular or CNS-mediated nausea.

Question 17

How are steroids used in management of nausea/vomiting

Answer 17

Dexamethazone is a glucocorticoid used in chemotherapy and peri-operative settings.

Reduce peri-tumoural oedema in cases of raised intracranial pressure secondary to brain tumour. Higher pressure results in nausea.

Question 18

What are the short and long term side effects of using glucocorticoids to manage nausea in raised intra-cranial pressure?

Answer 18

Short term - increased blood sugar, hunger, HTN

Long term - osteoporosis, diabetes mellitus

Question 19

What is the action of aprepitant?

Answer 19

Aprepitant is a neurokinin (NK-1) receptor antagonist

It blocks the effect of substance P, preventing emetic signals from being transmitted.

It crosses the BBB.

Question 20

What is fosaprepitant?

Answer 20

Fosaprepitant is the IV prodrug of aprepitant.

It is metabolised to aprepitant with a half life of two minutes - very rapid.

Aprepitant is otherwise adminstered orally.

Question 21

What is the action of the Hyoscine group of drugs?

Answer 21

Anticholinergic drugs at muscarinic receptors, also have minor histamine and serotonin antagonism

Question 22

What is the difference between Buscopan and Kwells? (Hyoscine drugs)

Answer 22

Buscopan = hyoscine butylbromide

Used to relieve stomach and bladder cramps/spasms. Not an effetive antiemetic

Kwells = hyoscine hydrobromide

Crosses the BBB - an effective antiemetic.

Question 23

What is the action of cyclizine?

Answer 23

Histamine antagonist, with main action at the CTZ.

Useful when the histamine pathway is involved e.g. in motion sickness, bran metastasis

Question 24

What is the action of lorazepam?

Answer 24

Very potent benzodiazepine, binds to CNS.

Used in anticipatory nausea associated with chemotherapy.

As it is a benzodiazepine, involved sedation as a side effect.

Question 25

Which drugs are safe to use in pregnancy to manage nausea/vomiting?

Answer 25

Cat A drugs = lots of human experience that it is not harmful

Examples: Metoclopramide, Pyridoxine

Question 26

What is the mainstay of treatment for children with nausea/vomiting?

Answer 26

Key focus is rehydration, avoiding mediations.

This is due to high rate of extrapyramidal symptoms from dopamine antagonism.