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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
For what patients is metoclopramide good for?
* Patients with GORD * Patients with Ileus (lack of movement in the gut)
26
What are some of the side effects of Metoclopramide?
* **Galactorrhoea** - via prolactin release * **Extra pyramidal side effects** - dystonia, parkinsonism
27
Explain how domperidone works?
* 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
Which patients is domperidone particularly good for?
For improving **lactation** in breastfeeding mothers if struggling with milk supply due to **increased prolactin** release
29
What are some of the side effects of domperidone?
* Sudden cardiac death (long QT and VT) * Galactorrhoea
30
Name 2 antipsychotics that also work as anti-emetics by post synatpic D2 receptor antaongism act on the CTZ?
* Haloperidol * Chlorpromazine
31
Name 2 corticosteroids that have an antiemetic effect by working on th CTZ
* Dexamethasone * Methylprednisolone
32
For which patients would you consider prescribing corticosteroids as an anti-emetic?
* Perioperative nausea and vomiting * Chemotherapy * Palliation (if stuggling to eat/ stay awake)
33
What are some of the side effects of using corticosteroids as an antiemetic?
* Insomnia * Increased appetite * Increased blood sugar
34
What are some of the side effects of using cannabinoids as an antiemetic?
* Dizziness * Drowsiness
35
Give an example of a Neurokinin 1 receptor antagonist
Aprepitant
36
Explain how neurokinin 1 receptor antagonists work as anti-emetics
* Prevent the action of **substance P** at the CTZ and peripherally * Boost the effects of 5HT3 receptor antagonists * Have anxiolyttic and antidepressant properties
37
What are some of the side effects of neurokinin 1 receptor antagonists?
* Headache * Diarrhoea/ constipation * Stevens - Johnson syndrome
38
For which patients would you use prokinetics (Domperidone, Metoclopramide) and which should you avoid using them for?
**Useful for:** * GORD * Ileus **Don't use:** * Obstruction * Risk of perforation
39
What is hyperemesis gravidarum? What causes it?
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
What are some of the risk factors for post operative nausea and vomiting?
**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
Describe the stages of the bristol stool chart
42
Name 3 opiod receptor agonists that can be used as antidiarrhoeals?
* Loperamide * Codeine * Morphine
43
Describe the MoA of Loperamide (e.g. Imodium)
* 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
What are some of the effects of using codeine and morphine as antidiarrhoeals?
* Paralytic ileus * Nausea and vomiting * Sedation * Addiction
45
Describe the principles of the constipating diet
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
What lifestyle changes can be made to help with constipation?
* Drink more water * Increase fibre intake - wholegrain food, fruit and veg, nuts, pulses * Regular exercise * Toilet routine and positioning
47
Explain the principles of osmotic laxatives
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
Name 2 osmotic laxatives
* Lactulose * Movicol - safer to use (up to 12 sachets a day)
49
Explain the principles of stimulant laxatives
* **Increase intestinal motility** * **Increase water and electrolye transfer in lower bowel** * Given orally or per rectum * Used is osmotic laxatives haven't worked
50
Name 3 stimulant laxatives
* Bisacodyl * Docusate sodium - stimulant and stool softener * Glycerin suppositories - cause rectal irritation and lubrication
51
Name 2 bulk forming laxatives
Ispaghula husk Methylcellulose
52
How do bulk forming laxatives work?
* Medicinal fibre - should try getting it from diet first * Increases fecal bulk * Hydrophilic action causes gut lumen to retain more water
53
Give examples of stool softeners
* Docusate sodium * Glycerin suppository * Arachis oil * Liquid paraffin
54
How do stool softeners work?
* Decrease surface tension of stool * Increase penetration of fluid into stool

Clinical Pharmacology (25 decks)

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