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Pharmacology > Antiemetics > Flashcards

Antiemetics Flashcards

1
Q

What is the mechanism of emesis?

A 
Nausea, salivation and sweating 
Retrograde peristalsis (stomach and duodenum)
Deep inspiration
Glottis closes 
Abdominal muscles contract
LOS relaxes
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2
Q

Where is the chemoreceptor trigger zone?

A

Medulla

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3
Q

What triggers the CTZ?

A

Direct triggers
Visceral afferent from gut
Vestibular nuclei
Sensory afferents via midbrain

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4
Q

What antiemetic agents work on the vestibular nuclei?

A

Muscarinic receptor antagonists

H1 receptor antagonists

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5
Q

How do muscarinic receptor antagonists work?

A

Competitive blockade of muscarinic Ach receptors at the vestibular nuclei and CTZ

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6
Q

Name the main muscarinic receptor antagonist

A

Hyoscine hydrobromide

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7
Q

Muscarinic receptor antagonists are good for?

A

People who cant take tablets- also give sub/cut
Motion sickness
Bowel obstruction (also works on other muscarinic receptors)

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8
Q

What are the side effects of hyoscine hydrobromide?

A

Sedation
Memory problems
Glaucoma
Dry mouth and constipation

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9
Q

Name a H1 receptor antagonist

A 
Cyclizine 
Promethazine 
Cinnirazine 
Diphenhydramine 
Levomepromazine
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10
Q

How do H1 receptor antagonists work?

A

Acts on the vestibular nuclei, inhibiting histeminergic signals to the CTZ

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11
Q

What are H1 receptor antagonists good for?

A

Motion sickness

Morning sickness - promethazine

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12
Q

Cyclizine should not be given to which patients?

A

Children

Elderly

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13
Q

What are the side effects of H1 receptor antagonists?

A

Sedation
Excitation
Cardiac toxicity - long QT interval
Antimuscarinic - dry mouth, constipation, urinary retention

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14
Q

Which agents work on visceral afferents in the gut?

A

5HT3 receptor antagonists

D2 receptor antagonists

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15
Q

How does serotonin act in the gut?

A

95% of serotonin in the body is within the gut, produced by enterochromaffin cells.
In response to parasympathetic stimulation, excites enteric neurones;
- smooth muscle to increase motility
- increase secretions
-regulate appetite

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16
Q

How are serotonin receptor antagonists effective?

A

Reduce GI motility and secretions

Centrally they act to inhibit the CTZ

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17
Q

What are the side effects of serotonin antagonists?

A 
Constipation
Headache 
Elevated liver enzymes 
Long QT syndrome 
Extra-pyramidal effects
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18
Q

Name a serotonin receptor antagonist

A

Ondansetron
Granesitron
Palonosetron

19
Q

What are the two D2 receptor antagonists?

A

Metoclopramide and domperidone

20
Q

How does metoclopramide work?

A

Increased ACh at muscarinic receptors in the gut, increases peristalsis.
Promotes gastric emptying by:
- increases tone at LOS
- increases tone and amplitude of gastric contractions
-decrease tone of pyloric

21
Q

What is D2 receptor antagonists good for?

A

GORD

Ileus

22
Q

What are the possible side effects of metoclopramide?

A

Galactorrhea via prolactin release

Extra-pyramidal effects

23
Q

What are the side effects of domperidone?

A

Sudden cardiac death - long QT and VT

Galactorrhoea

24
Q

What is the mechanism of domperidone?

A

Is similar to metoclopramide

25
Q

What is domperidone good for?

A

Improving lactation in breastfeeding mothers.

26
Q

What agents work on the CTZ?

A 
5HT3 receptor antagonists 
H1 receptor antagonists
Muscarinic receptor antagonists 
D2 receptor antagonists 
Corticosteriods
Cannabinoids
NK1 receptor antagonists
27
Q

Name a cannabinoid and its mechanism of action

A

Nabilone -Act on the CTZ

Good for chemotherapy - last line

28
Q

What are the side effects of cannabinoids

A

Dizziness

Drowsiness

29
Q

Name some corticosteroids which work on the CTZ

A

Dexamethasone

Methylprednisolone

30
Q

What are corticosteriods good for and what are their side effects?

A

Perioperative N&V
Chemotherapy
Palliation

Side effects:
Insomnia, increased appetite and blood sugar.

May have properties of D2 receptor antagonists

31
Q

Name a NK1 receptor antagonist

A

Aprepitant
Fosaprepitant
Netupitant

32
Q

How do NK1 receptor antagonists work?

A

Prevent action of substance P at CTZ and in peripheral nerves
Boosts effects of 5HT3 receptor antagonists
Anxiolytic and antidepressant properties.

Good for chemotherapy - delayed emesis

33
Q

What are the side effects of NK1 receptor antagonists

A
  • headache
  • diarrhoea/ constipation
  • Stevens-Johnson syndrome
34
Q

How do the D2 receptor antagonists work and name them?

A

Prochlorperazine
Chlorpromazine
Levomepromazine
Haloperidol

Act on the CTZ, may also block H1 and muscarinic receptors.

35
Q

What are the H1 receptor antagonists good for?

A

Motion sickness, vertigo

Prochlorperazine in pregnancy

36
Q

What are the side effects of D2 receptor antagonists?

A

Extra-pyramidal effects
Sedation
Hypotension

37
Q

What is haloperidol good for?

A

Chemotherapy and palliative care

38
Q

Domperidone ad metoclopramide can’t be used for?

A

Obstruction

Risk of perforation

39
Q

What is hyperemesis gravidarum and why is it dangerous?

A

Rapid rise in beta-HCG stimulate the CTZ, typically between 4-16 weeks. Higher risk with multiple pregnancies.

Risk of dehydration, weight loss, electrolyte imbalance, urinary ketones.

40
Q

What is the drug pathway for treating hyperemesis gravidarum?

A

Promethazine/prochlorperazine

Then metoclopramide

Then ondansetron (risk of cleft lip/palate)

41
Q

What is the pathway for chemotherapy anti-emetic agents?

A

Low risk- dexamethasone
Mod risk- dexamethasone + ondansetron
High risk- dexamethasone +ondansetron + anprepitant

For rescue, all use metoclopramide

42
Q

What are the post operative N&V risk factors?

A

Female
Young
Non-smoker
History of PONV or motion sickness

General anaesthetic
Use of volatile gas or NO
Po opioids

Duration of surgery
Laparoscopy

43
Q

What is the pathway for post operative anti-emetics?

A

Low risk- wait
Med risk- 1 or 2 agents
High risk - 2 agents

Pharmacology (22 decks)

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