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semester 4 - CPT & Prescribing > 19. Antiemetics > Flashcards

19. Antiemetics Flashcards

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1
Q

What is vomiting?

A

Involuntary, forceful expulsion of gastric contents through the mouth

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2
Q

What is the mechanism for vomiting?

A

Vomiting Centre in Medulla signals to vomit:

  1. Nausea, salivation, sweating
  2. Retrograde peristalsis
  3. Deep inspiration
  4. Closure of glottis
  5. Abdominal muscles contract
  6. Lower oesophageal sphincter relaxes
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3
Q

What is the chemoreceptor trigger zone?

A

Contains receptors that detect emetic agents in the blood and relays that information to the vomiting centre which is responsible for inducing the vomiting reflex

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4
Q

Where is the chemoreceptor trigger zone located?

A

Dorsal surface of the medulla at the caudal end of the fourth ventricle in a region known as the area postrema
- outside the blood brain barrier

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5
Q

What can stimulate the CTZ? (4)

A
  • sensory afferents via the midbrain
  • vestibular nuclei
  • visceral afferents from the gut (Vagus)
  • direct triggers (e.g. drugs)
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6
Q

What drugs act on the vestibular nuclei?

A
  • Muscarinic receptor Antagonists

- H1 receptor antagonists

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7
Q

Give examples of muscarinic receptor antagonist used to treat emesis. (2)

A

Hyoscine hydrobromide

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8
Q

How does Hyoscine hydrobromide work?

A

Competitive blockade of muscarinic acetylcholine receptors
• In the vestibular nuclei • Also at the CTZ
- block parasympathetic action

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9
Q

Who are Hyoscine hydrobromide good for?

A
  • People who can’t take tablets (available as a patch)
  • Motion sickness
  • Bowel obstruction
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10
Q

What are the side effects of hyoscine hydrobromide?

A
  • Sedation
  • Memory problems
  • Glaucoma
  • Dry mouth and constipation
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11
Q

Give examples of H1 receptor antagonists used to treat emesis.

A 
Cyclizine!
Levomepromazine! 
Cinnirazine 
Promethazine 
Diphenhydramine
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12
Q

How do H1 receptor antagonists work?

A

Centrally
• Acts on the vestibular nuclei
• Inhibits histaminergic signals from the vestibular system to the CTZ in medulla

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13
Q

What is the association between vestibular nuclei and emesis?

A

The vestibular nuclei are a group of four small special sensory nuclei in the lower pons and upper medulla for the vestibular nerve component of the vestibulocochlear nerve. movement of sterocilia on semicircular canals can stimulate the vestibular nerve leading to emesis like in motion sickness

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14
Q

Who are H1 receptor antagonists good for?

A

Good for :
• Motion sickness - long plane journeys
• Promethazine - morning sickness in pregnancy

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15
Q

Who is cyclizine not good for?

A

Little old ladies and children - can get disorientated and confused

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16
Q

What are the side effects of H1 receptor antagonists?

A
  • Sedation
  • Excitation
  • Antimuscarinic - dry mouth, constipation, urinary retention,
  • Cardiac toxicity (long QT interval)
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17
Q

What drugs act on the visceral afferents from the gut?

A
  • 5HT3 receptor Antagonists

- D2 receptor antagonists

18
Q

Where is most the serotonin in the body located and what is it produced by here?

A

95% serotonin in the body is located in the gut

• Produced by the enterochromaffin cells

19
Q

WHat is serotonin produced in response to in the gut?

A

In response to parasympathetic stimulation,

20
Q

what is the action of serotonin?

A

serotonin excites enteric neurones
• Smooth muscle contraction increases motility (except in the stomach)
• Increases gut secretions
• Regulates appetite

21
Q

Give examples of 5HT3 receptor Antagonists used to treat emesis

A

Ondansetron!
Granisetron
Palonosetron

22
Q

What are the effects of 5HT3 receptor Antagonists?

A 
Peripherally 
• Reduces GI motility 
• Reduces GI secretions 
Centrally 
• Acts to inhibit the CTZ
23
Q

Who are 5HT3 receptor Antagonists good for?

A

Almost everyone - it’s often the 1st line treatment

24
Q

What are the side effects of 5HT3 receptor Antagonists?

A 
Side effects - uncommon 
• Constipation 
• Headache 
• Elevated liver enzymes 
• Long QT syndrome 
• Extra-pyramidal effects - dystonia, parkinsonism
25
Q

Give examples of D2 receptor antagonists that act on visceral afferents of gut? (2)

A

Metoclopramide, Domperidone

26
Q

What are the effects of metoclopramide?

A

• Increases acetylcholine at muscarinic receptors in the gut
Promotes gastric emptying:
• ↑ tone at lower oesophageal sphincter so it closes
• ↑ tone and amplitude of gastric contractions
• ↓ tone of pylorus so it opens
• Increases peristalsis

27
Q

What is metoclopramide good for?

A
  • GORD

* Ileus

28
Q

What is ileus?

A

lack of peristalsis

29
Q

What are the side effects of metoclopramide?

A
  • Galactorrhoea via prolactin release

* Extra-pyramidal effects - dystonia, parkinsonism

30
Q

What are the effects of domperidone?

A

• Similar mechanism as metoclopramide

not used as much - significant cardiac side effect

31
Q

what are the side effects of domeperidone?

A
  • Sudden cardiac death (long QT and VT)

* Galactorrhoea

32
Q

what is domperidone good for?

A

Improving lactation in breastfeeding mothers

33
Q

When should prokinetics not be used?

A
  • bowel obstruction

- risk of perforation

34
Q

What drugs act directly on the CTZ? (7)

A
  • 5HT3 receptor antagonists
  • H1 receptor antagonists
  • Muscarinic receptor antagonists
  • D2 receptor antagonists
  • Corticosteroids
  • Cannabinoids
  • NK1 receptor antagonists
35
Q

Give examples of D2 receptor antagonists that act directly on the CTZ. (4)

A

Prochlorperazine
Chlorpromazine !
Levomepromazine
Haloperidol !

36
Q

what are The ‘zine’s good for?

A

Motionsickness,vertigo.

37
Q

action of the The‘zine’s?

A
  • Act on the CTZ

* May also block H1 and Muscarinic receptors

38
Q

which of the zines is used in pregnancy?

A

Prochlorperazine

39
Q

What is haloperidol used for?

A

Good for:-chemotherapy and palliation

40
Q

What are the side effects of these D2 receptor antagonists?

A

• Extra-pyramidal effects - dystonia, parkinsonism • Sedation • hypotension

semester 4 - CPT & Prescribing (25 decks)

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