Anti-emetics

Question 1

Outline the mechanism for chemo-induced nausea and vomiting (CINV)

Answer 1

cisplatin toxic to enterechromaffin cells (ECs) –> free radical release –> excessive 5HT release –> activates 5HT3A receptors on nerve fibres to NTS, CTZ and VC

Question 2

How do you treat CINV?

Answer 2

Ondansetron –> 5HT3A receptor antagonist
Glucacorticoids –> free radical production
Aprepitant –> neurokinin-1 receptor antagonist

Question 3

Outline the mechanism of motion sickness

Answer 3

neural mismatch between auditory labyrinth + vestibular system –> increased hypothalamic histamine release –> H1 receptors activated in CTZ –> vest. system + hypothal. also activate VC through cholinergic system

Question 4

How do you treat motion sickness?

Answer 4

Promethazine –> H1 receptor antagonist

Hyoscine (scopolomine) –> non-selective muscarinic receptor antagonist

Question 5

What is gastroparesis?

Answer 5

delayed stomach emptying which causes nausea + vomiting

Question 6

Outline the mechanism of vomiting due to gastroparesis

Answer 6

delayed stomach emptying –> decreased stomach contraction –> excessive 5HT release –> activates 5HT receptors on nerve fibres to VC (*contains D2 receptors) + CTZ

Question 7

How do you treat vomiting due to gastroparesis?

Answer 7

Metoclopramide –> D2 receptor antagonist –> inhibits D2 receptors in VC + increases gastric emptying
5HT3A receptor antagonists eg. Ondansetron –> inhibits CTZ

Question 8

What side effects would you associate with muscarinic receptor antagonism?

Answer 8

dry mouth

Question 9

What side effects would you associate with histamine H1 receptor antagonism?

Answer 9

drowsiness

Question 10

What side effects would you associate with dopamine D2 receptor antagonism?

Answer 10

extra-pyramidal side effects

Question 11

What side effects would you associate with 5HT3A receptor antagonism?

Answer 11

headaches