Anti-emetics HR Flashcards Preview

Y2 LCRS Pharm Fwong COPY > Anti-emetics HR > Flashcards

Flashcards in Anti-emetics HR Deck (16)
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1
Q

How can chemotherapy bring about a feeling of motion sickness?

A

Cisplatin:

  1. Binds gastric enterochromaffin cells
  2. Free radicals released
  3. Subsequent excessive 5HT release
  4. activates 5HT3A receptors on fibres to NTS which then goes to vomiting centre. Also activates fibres to CTZ which then go to VC (direct and indirect effects)
2
Q

What is the cause of motion sickness?

A

Neural mismatch between auditory labyrinth and CNS

3
Q

Recall the communication between the labyrinth and the CNS

A
  1. Signal from labyrinth to vestibular system. (muscarinic receptors on vestibular system)
  2. Signal from vestibular system to hypothalamus
  3. Hypothalamus releases histamine. Histamine agonises H1 Receptors in the CTZ
  4. CTZ communicates with VC, which then causes vomiting.

Note: there are projections from vestibular system and hypothalamus to VC which binds to muscarinic receptors on VC

4
Q

How can gastroparesis bring about the feeling of motion sickness?

A

More contents in stomach due to reduced emptying. This causes increased serotonin (5-HT) in stomach – activates 5-HT3A receptors on:

  1. Nerves fibres from stomach to vomiting centre (VC) which releases dopamine and acts on D2 receptors in the VC
  2. Nerve fibres to chemoreceptor trigger zone (CTZ)
5
Q

Recall the 4 main classes of anti-emetic and their principle uses

A

Antagonists of:

  1. 5HT3ARs - Chemotherapy induced N and V
  2. H1Rs - motion sickness
  3. D2Rs - gastroparesis induced N and V
  4. mAChRs - motion sickness (used with H1R antagonist)
6
Q

What sort of drug is used to treat chemotherapy-induced nausea and why?

A

5HT3AR antagonists. They reduce the nerve impulses to the CTZ, VC and NTS

7
Q

Give an example of a specific 5HT3AR antagonist

A

Ondasteron

8
Q

What is coadministered with ondasteron and why?

A

To increase efficacy coadminister with:

  • Glucocorticoid (reduces free radical production because they are anti-inflammatory)
  • Aprepitant (neurokinin 1 receptor antagonist)
9
Q

Give an example of a specific H1 receptor antagonist?

A

Promethazine

10
Q

Give an example of a muscarinic antagonist and recall its selectivity

A

Hyoscine

Will antagonise all types of mAChR at different concentrations

11
Q

What class of anti-emetic is used to treat gatroparesis-induced nausea and what are its ‘extra actions’ other than its main function?

A

D2 receptor antagonist
other actions:
1. Inhibits D2Rs in vomiting centre
2. Stimulates gastric emptying (prokinetic drug: increases motility of GIT)
3. Nb it also has partial 5HT3AR antagonist activity and so can also reduce the communication to CTZ from the stomach.

12
Q

Give an example of a D2R antagonists

A

Metoclopramide

13
Q

Describe the general side effects of anti-emetic drugs

A

Very non-specific in general

Often cause drowsiness

14
Q

Side effects of 5 HT3A receptor antagonists like ondansetron?

A

really ‘general’ side effects: constipation, headaches

15
Q

side effects of H1R antagonists and muscarinic receptor antagonists?

A

Histamine H1 receptor antagonists: drowsiness
Muscarinic receptor antagonists: drowsiness, dry mouth, constipation
note that they both cause drowsiness. They are often given together for motion sickness which is even worse.

16
Q

Side effect of D2R antagonists:

A

extrapyramidal side effects (blocks dopamine receptors on extrapyramidal motor pathways) and galactorrhea (dopamine normally inhibits prolactin release)