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CPT > L17 - Antiemetics > Flashcards

L17 - Antiemetics Flashcards

1
Q

Vomiting

A

Involuntary forceful expulsion of gastric contents through the mouth

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2
Q

Regurgitation

A

Passive overflow of gastric or oesophageal contents

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3
Q

Mechanism of vomiting

A
  1. Stimulus stimulates the vomiting centre in the medulla (chemoreceptor trigger zone)
  2. Nausea is felt with increased salivation and sweating
  3. Retrograde peristalsis of small bowel also causes nausea
  4. Deep inspiration
  5. Closure of glottis - prevents aspiration
  6. Abdominal muscles contract
  7. Lower oesophageal sphincter relaxes
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4
Q

What stimulates the chemoreceptor trigger zone in the medullar?

A
  1. Sensory afferents via the midbrain
    - squeamish
  2. Vestibular nuclei
    - inner ear infections
    - motion sickness
    - sea sickness
    - vertigo
  3. Visceral afferent form the gut
    - problem with gut transmits via vagus nerve
  4. Direct triggers
    - drugs - chemotherapy, anaesthetics, opiates
    - hormones - B- HCG
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5
Q

Chemoreceptor trigger zone

A
  • In blood side of the blood brain barrier

- located on the floor of the fourth ventricle within the area postrema

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6
Q

Drugs acting on the vestibular nuclei

A
  • muscarinic receptor antagonists

- H1 receptor antagonists

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7
Q

Drugs acting on the visceral afferent from the gut

A

Serotonin antagonists

D2 receptor antagonists

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8
Q

Drugs that act directly on the CTZ

A 
D2 receptor antagonists 
Serotonin receptor antagonist 
Muscarinic receptor antagonis5 
H1 receptor antagonist 
Corticosteroids
Cannabinoids 
NK1 receptor antagonist
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9
Q

Muscarinic receptor antagonist example

A

Hyoscine hydrobromide

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10
Q

Muscarinic receptor antagonist mechanism of action

A

Competitive blockade of muscarinic acetylcholine receptors

  • in the vestibular nuclei
  • in the CTZ
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11
Q

When are muscarinic receptor antagonists used

A

People who can’t take tablets - patch
Motion sickness
Bowel obstruction - reduce parasympathetic activity in the gut

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12
Q

Side effects of hyoscine hydrobromide

A 
Sedation 
Memory problems
Glaucoma 
Dry mouth 
Constipation
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13
Q

H1 recepteor antagonists

A 
Cyclizine 
Levomepromazine 
Cinnirazine 
Promethazine 
Diphenhydramine
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14
Q

H1 receptor antagonist mechanism of action

A

Acts on:

- vestibular nuclei x inhibits the histaminergic signals from the vestibular system to the CTZ in the medulla

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15
Q

When is H1 receptor antagonists used

A

Motion sickness - long plane journeys

Promethazine - morning sickness in pregnancy

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16
Q

What is cyclizine bad for

A

For little old ladies and children
Causes excitation and wacky-ness
Driving

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17
Q

Side effects of H1 receptor antagonists

A

Sedation
Excitation
Anti- muscarinic - dry mouth, constipation and urinary retention
Cardiac toxicity - long QT

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18
Q

Serotonin action in the gut

A

95% of serotonin is in the gut - produced by enterochromaffin cells due to parasympathetic stimulation

Serotonin excites enteric neurones for:

  • smooth muscles contraction - increases motility except stomach
  • increases gut secretions
  • regulates appetite
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19
Q

Serotonin receptor antagonist examples

A

Ondansetron - most common
Granesitron
Palonosetron

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20
Q

Mechanisms of action of serotonin receptor anatagonists

A

Centrally:
- inhibits the CTZ

Peripherally:

  • reduces gut motility - prevents retrograde peristalsis
  • reduces gut secretions - decreases volume of the vomit

Use:
- good for almost everyone - 1st line

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21
Q

Side effects of serotonin receptor antagonists

A 
Constipation 
Headache 
Elevated liver enzymes 
Long QT syndrome 
Extra-pyramidal effects - dystonia and Parkinsonism
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22
Q

D2 receptor antagonist examples

A

Metoclopramide
Domperidone

Prochlorperazine
Levomepromazine
Chlorpromazine
Haloperidol

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23
Q

Mechanism of action of metoclopramide and domperidone

A
  • Increases acetylcholine at muscarinic receptors in the gut
  • increases parasympathetic activity
  • increases gastric emptying
  • increases tone of the lower oesophageal sphincter (closes)
  • increases tone and amplitude of gastric contractions - pushing food downs
  • decreases tone of the pylorus sphincter - opens allowing gastric emptying
  • increases peristalsis
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24
Q

When is metoclopramide used?

A

GORD

Ileus

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25
Ileus
Loss of muscle contraction therefore loss of peristalsis | Occurs post surgery or after a significant infection
26
Side effects of metoclopramide
Galactorrhoea - prolactin release | Extra pyramidal effects - dystonia, Parkinsonism
27
Domperidone use
Improving lactation in breastfeeding mothers as side effects is galactorrhoea - increased risk of sudden cardiac death - long QT and VT - not used commonly
28
Mechanism of action of the ‘zine’ D2 receptor antagonists
Act on the CTZ | Block H1 and muscarinic receptors as well
29
When are the zine D2 receptor anatagonists used
Motion sickness | Vertigo
30
When is prochlorperazine used
During pregnancy
31
When is Haloperidol used
Chemotherapy and palliation
32
Side effects of other D2 receptor anatagonists
Sedation Hypotension Extra pyramidal effects - dystonia and Parkinsonism
33
Corticosteroid examples
Dexamethasone | Methylprednisolone
34
Mechanism of action of corticosteroids and use
-assumed to act on CTZ and D2 receptors Use: - chemotherapy - palliation - appetite loss - perioperative nausea and vomiting
35
Side effects of corticosteroids
Insomnia Increased appetite Increased blood sugar - long term use can cause Cushing’s syndrome but corticosteroids are normally used short term
36
Cannabinoid example
Nabilone
37
Nabilone mechanism, use and side effects
Mechanism: assumed to act on CTZ Use: last line for chemotherapy nausea and vomiting Side effects: dizzying and drowsiness
38
Neurokinin 1 receptor anatagonists examples
Aprepitant Fosaprepitant Netupitant
39
Mechanism of nuerokinin -1 receptor antagonists
- Prevents the action of substance P at CTZ and in peripheral nerves - pain killer - Boosts effects of serotonin receptor antagonists - anxiolytics and antidepressant properties
40
When are neurokinin-1 receptor antagonists used
In delayed emesis with chemotherapy
41
Side effects of neurokinin-1 receptor antagonists
Headache Constipation or diarrhoea Steven Johnson syndrome
42
Motion sickness treatment
Give drug before trigger 1st line for plane journeys: - hyoscine hydrobromide - muscarinic receptor anatagonist (sedating) 1st line for driving: Cinnirazine - H1 receptor antagonist (fewer side effects)
43
Nasogastric tube
Mechanically decompress the stomach | Lets fluid out without vomiting
44
Prokinetics
Increases gut motility Examples: - domperidone - metoclopramide Used in: - GORD - Ileus Not used in: - obstruction - risk of perforation
45
Drugs for nausea
1st line - ondansetron - serotonin receptor antagonist AND/OR cyclizine- H1 receptor antagonists THEN Dexamethasone- corticosteroid Dexamethasone -
46
Hyperemesis gravidarum
Rapid rise in B-HCG stimulates the CTZ Typically in weeks 4-16 Higher risk with multiple pregnancies Causes: - more than morning sickness - dehydration - 5% weight loss - electrolyte imbalance - urinary ketones
47
Drugs for hyperemesis gravidarum
Promethazine - H1 receptor antagonist OR Prochlorperazine - D2 receptor antagonist THEN ADD Metoclopramide- D2 receptor antagonist and prokinetic THEN ADD Ondansetron - serotonin receptor antagonist
48
Ondansetron risk on pregnant ladies
If given in the 1st trimester, there is greater risk of cleft lip therefore last line
49
Drugs to treat chemotherapy risk of emesis
Low risk: - dexamethasone - rescue: metoclopramide Moderate risk: - dexamethasone - and ondansetron - rescue: metoclopramide High risk: - dexamethasone - and ondansetron - and aprepitant - rescue: metoclopramide
50
Post operative nausea and vomiting risk factors
``` Female History of post operative N+V Young Non smoker General anaesthetic + use of nitrous oxide Post operative opioids Duration of surgery Laparoscopy ```
51
Infective gastroenteritis
Viral, bacterial or protozoan - can be osmotic or secretory - May be toxin mediated
52
How to treat diarrhoea
- treat the cause e.g. Crohn’s disease - increase transit time - increase comfort - minimise sore bottom - prevent incontinence
53
Medication to treat diarrhoea
Opioid receptor antagonists: - loperamide - codeine - morphine
54
Loperamide
1st line Specific to MOP in the myenteric plexus of the gut (less side effects) - decreases tone of the longitudinal and circular smooth muscle - reduces peristalsis - increases segmental contractions (shuttling) - gut contents are in contact with enterocytes for longer - decreases colonic mass movement by suppressing the gastrocolic reflex
55
Side effects of opioid receptor antagonists
- paralytic ileus - nausea and vomiting - sedation - addiction (codeine and morphine)
56
Constipating diet
For long term loose stools - IBD, IBS, Short bowel, hyper mobility or dug side effect - bananas - white rice, bread or pasta - limit fruit to 3 per day - avoid caffeine, sorbitol, fatty or spicy foods and fizzy drinks - probiotics - low in fibre and high in potassium - binds to stool
57
Diet and life style changes to help constipation
- drink more water - increase fibre intake - fruit, pulses, nuts and veg + whole grains - regular exercise - toilet routine and positioning
58
Education for constipation
Laxatives: - osmotic - mush - stimulants - push - bulk forming - stool softener Enemas - osmotic - stimulant
59
Osmotic laxatives
Increase the amount of water in the large bowel - draw fluid in: lactulose - retain the fluid they came in with - macrogols
60
Macrogols
Movicol Cosmocol - take with squash, yoghurt and ice cream - safe an can take up to 12 sachets per day
61
Stimulant laxatives
- Increases the intestinal motility | - oral or per rectum
62
Stimulant laxative examples
``` Bisacodyl Sodium picosulphate Senna Co-danthromer Docusate sodium Glycerin ```
63
Docusate sodium
Stimulant and stool softener
64
Glycerin
Suppository | Causes rectal irritation and lubrication
65
Bulk forming laxative examples and mechanism
Ispagula husk Methylcellulose Acts as medicinal fibre to bulk stool - feel solid stool which triggers the gastrocolic reflex - can be used in constipation and diarrhoea
66
Stool softener
Mainly enemas Decreases surface tension of stool Increase penetration of fluid into stool - docusate sodium - glycerin suppository - arachis oil - liquid paraffin

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