2.1 Nausea and Vomiting

Question 1

What can nausea and vomiting stimulated by?

Answer 1

Toxins: alcohol, bacterial poisons 
Smells 
Motion sickness 
Migrane 
Pregnancy

Drug-induced:
Chemotherapy
Digoxin or theeophylline
Toxicity
SSRIs
Iron salts
Levodopa 
Opioids

Question 2

What are the physiological responses to vomiting?

Answer 2

1. Discomfort, dry mouth, salivary inhibition
2. Yawning- sympathetic distress
3. Reappearance of saliva
4. Pyloris closes
5. Tone of stomach increases
6. Deep breath
7. Contraction of abdominal muscles to force food out
8. Forced expiration to prevent inhalation

Question 3

Where does central regulation of vomiting occur?

Answer 3

Vomiting centre and the chemoreceptor trigger zone (CTZ)

Question 4

What is the CTZ sensitive to?

Answer 4

Chemical stimulation meaning it is the main site of anti-emetic drugs

Question 5

What stimulates the vomiting centre?

Answer 5

Output from the CTZ stimulated the vomiting centre, leading to the initiation of vomiting

Neuronal signals from the GIT feed into the CTZ and Vomiting centre

Question 6

What neurotransmitters are involved in nausea and vomiting ?

Answer 6

Histamine
ACh
Dopamine
5-HT

Blocking these receptors in the brain prevents nausea and vomiting

Question 7

Breifly decribe how chemotherapy agents stimulate nausea and vomiting ?

Answer 7

Cytotoxic drugs causes the release of 5-HT in the gyt.

This acts on the vagal afferent and circulating 5-HT stimulates the CTZ and NTS

Question 8

Name the types of anti-emetics available and an example of each

Answer 8

1. H1-Histamine receptor antagonists
   e. g Promethazine
   - Effective in motion sickness
   - Anti-muscarinic actions
   - Produces drowsiness

2. Anti-muscarinic agents 
eg Hyoscine 
- Effective in motion sickness 
- Reduce  gastric motility
- Antimuscarinic action (dry mouth)
- Produces drowsiness 

3. Dopamine antagonist
   e. g. domperidone,metoclopramide
   - Acts in CTZ but has unwanted CNS effects.
   - Effective against anticancer drug-induced nausea/vomiting
   - Also stimulates gastric emptying - reducing nausea
4. 5-hydroxytryptamine antagonist
   e. g Ondansetron
   - Blocks 5-HT and 5-HT3 receptor in gut and CNS
   - Very effective against anti-cancer drugs
   - Not effective in motion sickness
5. Canabanoid receptor agonist
   eg Nabilone
   - Licensed for chemotherapy
6. Neurokinin receptor antagonist
   e. g aprepitant
   - NK1 receptor activated by substance P
   - NK1 receptor antagonist supress nausea and vomiting
   - Used in combination with a 5-HT receptor antagonist for N&V in chemotherapy
7. Steroids
   e. g dexamethasone
   - Used in chemotherapy indiced N&V

Question 9

What is the standard prescription for chemotherapy?

Answer 9

5-HT receptor antagonist
+steroid
+ NK1 receptor asntagonist