Anti-emetics Flashcards
How can chemotherapy bring about a feeling of motion sickness?
Cisplatin:
- Binds gastric enterochromaffin cells
- Free radicals released
- Subsequent excessive 5HT release
- NTS in vomiting centre and CTZ activated (direct and indirect effects)
What is the cause of motion sickness?
Neural mismatch between auditory labyrinth and CNS
Recall the communication between the auditory labyrinth and the CNS
- Signal to hypothalamus from vestibular system
- Hypothalamus releases histamine
- Histamine agonises H1R in the CTZ
- CTZ activates vomiting centre via muscarinic receptors
How can gastroparesis bring about the feeling of motion sickness?
More contents in stomach, stimulates 5HT receptors in stomach that can directly trigger CTZ
Recall the 4 main classes of anti-emetic
Antagonists of:
- 5HT3ARs
- H1Rs
- D2Rs
- mAChRs
What sort of drug is used to treat chemotherapy-induced nausea and why?
5HT3AR antagonists
Blocks the effect of the excessive histamine release
Give an example of a specific 5HT3AR antagonist
Ondasteron
What is coadministered with ondasteron and why?
To increase efficacy coadminister with:
- Glucocorticoid (reduces free radical production)
- Aprepitant (neurokinin 1 receptor antagonist)
Give an example of a specific H1 receptor antagonist?
Promethazine
Give an example of a muscarinic antagonist and recall its selectivity
Hyoscine
Will antagonise all types of mAChR at different concentrations
What class of anti-emetic is used to treat gatroparesis-induced nausea and why?
D2 receptor antagonist
Reasons:
1. Inhibits D2Rs in vomiting centre
2. Stimulates gastric emptying
Give 2 examples of D2R antagonists
Metoclopramide
Domperidone
Describe the general side effects of anti-emetic drugs
Very non-specific in general
Often cause drowsiness
Recall a possible side effect associated with each of the classes of anti-emetic
- mAChR: dry mouth
- D2R: Extra-pyramidal
- 5HT3A: Constipation
- H1R: drowsiness
