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Clinical Pharmacology > Antiemetics and Antidiarrhoeals > Flashcards

Antiemetics and Antidiarrhoeals Flashcards

1
Q

What is vomiting?

A

Involuntary, forecul expulsion of gastric contents through the mouth

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2
Q

What is regurgitation?

A

The effortless bringing back up of food (not made it to the stomach)

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3
Q

What steps happen in the GI tract during vomiting?

A
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4
Q

What area of the brain causes vomiting. Where is this located?

A

Chemoreceptor trigger zone (CTZ)

In the floor of the 4th ventricle on the blood side of the blood brain barrier

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5
Q

What things act on the chemoreceptor trigger zone to cause vomiting?

A
  • Direct triggers e.g. drugs, hormones
  • Info from vestibular nuclei e.g. during motion sickness, vertigo
  • Visceral afferents from gut i.e. vagus nerve
  • Sensory afferents via midbrain e.g. sights and smells
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6
Q

What type of antiemetic drugs can act on the vestibular nuclei?

A
  • Muscarininic receptor antagonists
  • H1 receptor antagonists
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7
Q

What type of anti-emetics act on the visceral afferents from the gut?

A
  • 5HT3 antagonists
  • D2 receptor antagonists
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8
Q

What anti-emetic drugs act directly on the chemoreceptor trigger zone?

A
  • D2 receptor antaogonists
  • 5HT3 antagonists
  • Muscarinic receptor antagonists
  • H1 receptor antagonists
  • Corticosteroids
  • Cannabinoids
  • NK1 receptor antagonists
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9
Q

Give an example of a muscarinic receptor antagonist

A

Hyoscine hydrobromide

(tablet or transdermal)

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10
Q

How to muscarinic receptor antagonists work?

A

Competitively block muscarining Acetylcholine receptors

In the vestibular nuclei and the CTZ

ACh receptors part of parasympathetic nervous system

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11
Q

Which patients are muscarinic receptor antagonists good for?

A
  • People who can’t take tablets- patch form
  • Motion sickness
  • Bowel obstruction- patch form
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12
Q

What are some of the side effects of muscarinic receptor antaogonists?

A
  • Sedation
  • Memory problems
  • Glaucoma
  • Dry mouth and constipation
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13
Q

Name the most commonly used H1 receptor antagonist

A

Cyclizine

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14
Q

How do H1 receptor antagonists work?

A
  • Act on vestibular nuclei
  • Inhibit histaminergic signals from vestibular system to CTZ in the medulla
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15
Q

Which patients are H1 receptor antagonists good for?

A
  • Motion sickness- long plane journey (sedative effect helps sleep)
  • Promethazine is good for morning sickness in pregnancy
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16
Q

Which patients should you avoid using cyclizine in?

A
  • Old ladies
  • Children
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17
Q

What are some of the side effects of H1 receptor antagonists?

A
  • Sedation
  • Excitation
  • Antimuscarinic effects- dry mouth, consitpation, urinary retention
  • Cardiac toxicity (long QT interval)
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18
Q

Which cells in gut produce 5HT?

A

Enterochromaffin cells

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19
Q

What causes 5HT release in the gut? What are the effects of its release?

A
  • In response to parasympathetic stimulation
  • Serotonin excites enteric neurones causing:
    • Smooth muscle contraction (increasing motility)
    • Increased gut secretions
  • Regulates appetite
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20
Q

What are the effets of 5-HT3 receptor antagonists?

A

Peripherally:

  • reduces gut motility
  • reduces GI secretions

Centrally

  • Acts to inhibit the CTZ
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21
Q

Name the most commonly prescribed 5HT3 antagonist?

A

Ondansetron

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22
Q

What are some of the side effects of 5HT3 receptor antaogonists? (uncommon)

A
  • Constipation
  • Headache
  • Elevated liver enzymes
  • Long QT syndrome
  • Extra-pyramidal effects: dystonia, parkinsomism
23
Q

Name 2 D2 receptor antagonists

A
  • Metoclopramide
  • Domperidone
24
Q

Explain how Metoclopramide works

A
  • Increases Acetylcholine levels at muscarinic receptors in the gut
  • Promotes gastic emptying
    • Increases tone at LOS to stop reflux
    • Increaes tone and amplitude of gastric contractions
    • Decreases tone of pyloric sphincter so it opens letting food out
  • Increases perilstalsis
25
Q

For what patients is metoclopramide good for?

A
  • Patients with GORD
  • Patients with Ileus (lack of movement in the gut)
26
Q

What are some of the side effects of Metoclopramide?

A
  • Galactorrhoea - via prolactin release
  • Extra pyramidal side effects - dystonia, parkinsonism
27
Q

Explain how domperidone works?

A
  • Similar to metoclopramide- increases acetylcholine at muscarininic receptors in gut to promote gastric emptying
  • Used selectively due to increase risk of cardiac sid effects
28
Q

Which patients is domperidone particularly good for?

A

For improving lactation in breastfeeding mothers if struggling with milk supply

due to increased prolactin release

29
Q

What are some of the side effects of domperidone?

A
  • Sudden cardiac death (long QT and VT)
  • Galactorrhoea
30
Q

Name 2 antipsychotics that also work as anti-emetics by post synatpic D2 receptor antaongism act on the CTZ?

A
  • Haloperidol
  • Chlorpromazine
31
Q

Name 2 corticosteroids that have an antiemetic effect by working on th CTZ

A
  • Dexamethasone
  • Methylprednisolone
32
Q

For which patients would you consider prescribing corticosteroids as an anti-emetic?

A
  • Perioperative nausea and vomiting
  • Chemotherapy
  • Palliation (if stuggling to eat/ stay awake)
33
Q

What are some of the side effects of using corticosteroids as an antiemetic?

A
  • Insomnia
  • Increased appetite
  • Increased blood sugar
34
Q

What are some of the side effects of using cannabinoids as an antiemetic?

A
  • Dizziness
  • Drowsiness
35
Q

Give an example of a Neurokinin 1 receptor antagonist

A

Aprepitant

36
Q

Explain how neurokinin 1 receptor antagonists work as anti-emetics

A
  • Prevent the action of substance P at the CTZ and peripherally
  • Boost the effects of 5HT3 receptor antagonists
  • Have anxiolyttic and antidepressant properties
37
Q

What are some of the side effects of neurokinin 1 receptor antagonists?

A
  • Headache
  • Diarrhoea/ constipation
  • Stevens - Johnson syndrome
38
Q

For which patients would you use prokinetics (Domperidone, Metoclopramide) and which should you avoid using them for?

A

Useful for:

  • GORD
  • Ileus

Don’t use:

  • Obstruction
  • Risk of perforation
39
Q

What is hyperemesis gravidarum? What causes it?

A

Severe morning sickness with dehydration, 5% weight loss, electrolyte imbalance and urinary ketones

Caused by a rapid rise in Beta-HCG stimulating the CTZ

At higher risk with multiple pregnancies (twins, triplets)

40
Q

What are some of the risk factors for post operative nausea and vomiting?

A

Patient:

  • Female
  • Hx of PONV or motion sickness
  • Younger
  • Non smoker

Anaesthetic:

  • General > regional
  • Use of volatile anaesthesitc or NO
  • Post op opiods

Surgery:

  • Duration of operation
  • Laparoscopic surgery
41
Q

Describe the stages of the bristol stool chart

A
42
Q

Name 3 opiod receptor agonists that can be used as antidiarrhoeals?

A
  • Loperamide
  • Codeine
  • Morphine
43
Q

Describe the MoA of Loperamide (e.g. Imodium)

A
  • Specific to mui receptors of the myenteric plexus (gut specific)
  • Decreases tone of longitudinal and smooth muscle
  • Reduces perilstalsis
  • Decreases colonic mass movement
    Overall slowing transit time through gut
44
Q

What are some of the effects of using codeine and morphine as antidiarrhoeals?

A
  • Paralytic ileus
  • Nausea and vomiting
  • Sedation
  • Addiction
45
Q

Describe the principles of the constipating diet

A

Useful for those with long term loose stools (IBS, IBD, short bowel, hypermotility, drug side effects)

Eat foods such as:

  • Bananas - high in Potassium and fibre
  • White Rice - binds stools
  • White bread/ pasta - low in fibre

Limit fruit to 3 portions p/day

Avoid:

  • Caffeine, sorbitol, fatty/ spicy food and fizzy drinks
46
Q

What lifestyle changes can be made to help with constipation?

A
  • Drink more water
  • Increase fibre intake - wholegrain food, fruit and veg, nuts, pulses
  • Regular exercise
  • Toilet routine and positioning
47
Q

Explain the principles of osmotic laxatives

A

Increase the amount of water in the large bowel making stool less hard

Either by drawing fluid in (Lactulose)

or retaining fluid they came with (Macrogols)

48
Q

Name 2 osmotic laxatives

A
  • Lactulose
  • Movicol - safer to use (up to 12 sachets a day)
49
Q

Explain the principles of stimulant laxatives

A
  • Increase intestinal motility
  • Increase water and electrolye transfer in lower bowel
  • Given orally or per rectum
  • Used is osmotic laxatives haven’t worked
50
Q

Name 3 stimulant laxatives

A
  • Bisacodyl
  • Docusate sodium - stimulant and stool softener
  • Glycerin suppositories - cause rectal irritation and lubrication
51
Q

Name 2 bulk forming laxatives

A

Ispaghula husk

Methylcellulose

52
Q

How do bulk forming laxatives work?

A
  • Medicinal fibre - should try getting it from diet first
  • Increases fecal bulk
  • Hydrophilic action causes gut lumen to retain more water
53
Q

Give examples of stool softeners

A
  • Docusate sodium
  • Glycerin suppository
  • Arachis oil
  • Liquid paraffin
54
Q

How do stool softeners work?

A
  • Decrease surface tension of stool
  • Increase penetration of fluid into stool

Clinical Pharmacology (25 decks)

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