Anti-emetics Flashcards

1
Q

describe the vomiting pathway

A
  • deep breath, glottis closes, larynx rises to open upper oesophageal sphincter
  • soft palate elevates
  • diaphrgam contracts sharply to create -ve intrathoracic pressure
  • facilitates sphincter opening
  • abdo walls contract as well to squeeze stomach and raise intra-gastric pressure
  • pylorus closed
  • upper sphincters opens
  • pressure escapes proximally
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2
Q

what does cisplatin do? which cells particularly associated with nausea?

A
  • kills quickly replicating cells
  • has impact on enterochromaffin cells
  • these cell apoptose
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3
Q

what happens when these cells apoptose?

A
  • release excessive 5-HT

- also release free radicals

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4
Q

What is the 5-HT3aR? where is it expressed?

A
  • receptors of 5-HT
  • expressed on loads of cells
  • IMPORTANT:
  • on nerve fibres to nucleus tractus solitarius
  • on nerve fibres to vomiting centre
  • on nerve fibres to CTZ
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5
Q

describe the location of the CTZ and its significance

A
  • CTZ closely associated to VC on brainstem
  • outside of BBB so can detect signals in blood
  • detect signals outside BBB and send it into VC
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6
Q

what is the treatment of chemo-induced nausea?

A
  • ondansetron (5HT3A receptor antagonist)

- blocks signals and so reduces nausea and vomiting by chemo

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7
Q

what should ondansetron be coadministered with?

A
  • glucocorticoid: reduce free radical production

- aprepitant: neurokinin-1 receptor antagonist (reduce free radicals)

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8
Q

where does motion sickness originate?

A
  • labyrinthe
  • neural mismatch
  • labyrinthe projects to vestibular system via muscarinic receptors
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9
Q

how is the hypothalamus involved in motion sickness pathway?

A
  • labyrinthe somehow connected to hypothalamus
  • in hypothalamus, get inc. hypothalamic histamine release (H)
  • activated H1 receptors in CTZ
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10
Q

how do the vestibular system and hypothalamus activate VC?

A

through cholinergic system

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11
Q

what is the treatment of motion sickness?

A
  • promethazine: H receptor antagonist

- Hyoscine: non selective muscarinic receptor antagonist

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12
Q

what is gastroparesis?

A
  • delayed emptying of stomach
  • get vomiting due to unknown cause, abdo pain, bloating
  • get reduced stomach contraction –> 5-HT
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13
Q

how does this trigger vomiting?

A
  • direct fibres contact to vomiting centre
  • 5HT activated 5-HT3a receptors on nerve fibres to VC
  • activates these receptors to CTZ
  • also get dopamine release which acts on D2 receptors on VC
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14
Q

how do you treat this nausea?

A
  • metoclopramine

- 5HT3aR antagonist

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15
Q

what is the MoA of metoclopramine?

A
  • dopamine D2 receptor antagonist
  • stimulates gastric emptying
  • inhibits D2 receptors in VC
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16
Q

what is the MoA of 5HT3a receptor antagonist?

A

inhibits activation of CTZ

17
Q

summarise the physiological control of nausea and vomiting

A
  • vomiting centre: innervated by nucleus of tractus solitarius
  • CTZ: communicated w/ vomiting centre
18
Q

what are the side effects of D2 receptor antagonists?

A
  • drowsiness
  • dizziness
  • anxiety
  • extra-pyramidal reactions
  • hyperprolactinaemia
  • galactorrhoea
  • disorder of menstruation
19
Q

what are the side effects of muscarinic receptor antagonists?

A
  • drowsiness
  • dry mouth
  • cycloplegia
  • constipation
  • mydriasis
20
Q

what are the unwanted side effects of serotonin receptor antagonists?

A
  • headache
  • sensation of flushing and warmth
  • constipation (inc. large bowel transit time)