Anti-Emetics

Question 1

State the 4 major classes of anti-emetic drugs.

Answer 1

5-HT3A receptor antagonists
Histamine H1 receptor antagonists
Muscarinic receptor antagonists
Dopamine (D2) receptor antagonists

Question 2

What is special about the location of the CTZ and vomiting centre?

Answer 2

In a part of the brain that has a very porous BBB

So act as an early warning system to protect the brain from toxin damage

Question 3

Describe the pathophysiology of chemotherapy induced nausea and vomiting

Answer 3

Drug is toxic to enterochromaffin cells in gastric antrum, stimulates excessive release of 5HT
5HT binds to 5HT 3A receptors on nerve fibres to chemoreceptor trigger zone
CTZ activates nerve fibres to the vomiting centre, inducing nausea + vomiting

Question 4

What class of drug is primarily used for chemotherapy induced nausea and vomiting? Give an example

Answer 4

5HT 3A receptor antagonist

Ondansetron (as part of triple therapy with glucocorticoid + neurokinin 1 receptor antagonist)

Question 5

Describe the pathophysiology of motion sickness

Answer 5

Neural mismatch in the labyrinth activates histamine receptors on vestibular nuclei
Vestibular nuclei activate muscarinic receptors on CTZ
CTZ activates VC, causing nausea

Question 6

Name 2 classes of drugs indicated for treatment of motion sickness. Give examples of each.

Answer 6

H1 receptor antagonist e.g. Promethazine (inhibits H1 stimulation in vestibular nuclei)
Non-selective muscarinic receptor antagonists e.g. Hyoscine (inhibit muscarinic stimulation of CTZ + VC)

Question 7

What is gastroparesis? What does this cause associated with nausea and vomiting?

Answer 7

Delayed emptying + lack of contraction of the stomach

Excessive release of 5HT, which activates 5HT 3A receptors on CTZ + stimulates activation of VC

Question 8

Give an example of a drug used to treat nausea and vomiting associated to gastroparesis? Describe its mechanism of action.

Answer 8

Metoclopramide
D2 receptor antagonist (pro kinetic, stimulates gastric emptying + inhibits D2 receptors in VC)
5HT 3A receptor antagonist (inhibits activation of CTZ)

Question 9

What class of drug can be useful in treating drug induced nausea and vomiting e.g. in Parkinsons disease?

Answer 9

D2 antagonists

Question 10

List 6 mechanic triggers for nausea and vomiting

Answer 10

Chemotherapy induced
Drug induced e.g. in PD
Motion sickness
Gastrointestinal problems
Pregnancy 
Traumatic incident

Question 11

List 2 side effects of muscarinic receptor antagonists

Answer 11

Drowsiness

Dry mouth

Question 12

List 2 side effects of D2 receptor antagonists

Answer 12

Galactorrhoea

Extrapyramidal symptoms

Question 13

What side effect is caused by H1 receptor antagonists?

Answer 13

Drowsiness (which can be desirable)

Question 14

List 2 side effects of 5HT 3A receptor antagonists

Answer 14

Headaches

Constipation