anti-emetics

Question 1

how does chemotherapy induce nausea and vomiting?

Answer 1

cisplatin is toxic to ECL cells by release of free radicals

the free radicals cause 5-HT release which activates 5-HT3a nerve fibres which go to the chemoreceptor trigger zone

the CTZ activates nerves to the vomiting centre which causes nausea and vomiting

Question 2

what treatment may be given to chemotherapy induced nausea & vomiting

Answer 2

triple therapy:

5-HT3a receptor antagonist- ONDANSETRON

reduce free radical production- GLUCOCORTICOIDS (also reduces inflammatory response caused by chemotherapy)

neurokinin 1 receptor antagonists. primarily expressed on the vomiting centres- APREPITANT

Question 3

what is the pathophysiology of motion sickness?

Answer 3

there is a neural mismatch within the labyrinth which activates histamine receptors on the vestibular nuclei

the vestibular nuclei activate muscarinic receptors on the chemoreceptor trigger zone –> vomiting centre

Question 4

what treatment may be given for motion sickness?

Answer 4

H1 receptor antagonist- PROMETHAZINE

non-selective muscarinic receptor antagonist - HYOSCINE/ SCOPOLOMINE

drugs not used ONLY for motion sickness

Question 5

what may be the pathophysiology of vomiting due to an unknown cause

Answer 5

gastroporisis- delayed emptying of the stomach
reduced stomach contraction

5-HT activates receptors on CTZ–> VC –> nausea

high levels of dopamine in the system can result in nausea and vomiting as there are receptors located on the CTZ

Question 6

what is the MOA of metoclopramide

Answer 6

dopamine D2 receptor antagonist

5-HT3a receptor antagonist

Question 7

what are the main classes of anti emetic drugs?

Answer 7

5-HT3A receptor antagonists

Histamine H1 receptor antagonists

Muscarinic receptor antagonists

Dopamine D2 receptor antagonists

Question 8

what are some side effects of Muscarinic receptor antagonists?

Answer 8

drowsiness

dry mouth

Question 9

what are the possible side effects of Histamine H1 receptor antagonists

Answer 9

drowsiness

may be beneficial if treating motion sickness because you would want to go to sleep

Question 10

possible side effects of Dopamine D2 receptor antagonists ?

Answer 10

galactorrhoea

extrapyramidal side effects

Question 11

possible side effects with 5-HT3A receptor antagonists

Answer 11

constipation

headaches