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Pharmacology > 21) Antiemetics > Flashcards

21) Antiemetics Flashcards

1
Q

Define Vomiting ?

A

Involuntary forceful expulsion of gastric contents through the mouth

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2
Q

What happens during vomiting ?

A

1) Nausea, Salivation and Sweating
2) Retrograde Peristalsis
3) Deep Inspiration
4) Closure of Glottis
5) Abdominal Muscles Contract
6) Lower Oesophageal Sphincter

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3
Q

What can trigger the Vomiting Centre ?

A

1) Sensory Afferent via midbrain ( Seeing something gross , Horrible taste )
2) Vestibular Nuclei
3) Visceral Afferents from Gut (Stretched, Inflamed)
4) Direct Triggers (Drugs, Toxins, Hormones)

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4
Q

What two agents act on the Vestibular Nuclei ?

A

1) Muscarinic Receptor Antagonists

2) H1 Receptor Antagonists

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5
Q 
Outline the features of Muscarinic Receptor Agonists:
> Example
> Mechanism of Action
> When is it Used 
> Side effects
A

Example:
> Hyoscine Hydrobromide

MOA:
> Competitive blockade of msucarinic Ach receptors in the Vestibular Nuclei and at the Vomiting Centre

When is it used:
> People who can’t take tablets (Patch)
> Motion Sickness
> Bowel Obstruction

Side Effects:
> Sedation 
> Memory problems 
> Glaucoma 
> Dry mouth 
> Constipation
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6
Q 
Outline the features of H1 Receptor Antagonists 
> Example 
> MOA 
> When is it used 
> Side Effects
A

Examples:
> Cyclizine
> Levomepromazine

Mechanism of Action:
> Acts on the Vestibular nuclei inhibiting histaminergic signals from the vestibular system to the ctz in the medulla

When is it used:
> Motion sickness
> Promethazine - Morning sickness in pregnancy

Side Effects 
> Cyclizine has greater side effects on elderly and children 
> Sedation
> Excitation 
> Anti muscarinic effects 
> Cardiac Toxicity
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7
Q

Which agents act on visceral afferents in the gut ?

A

> Serotonin (5HT) Receptor antagonists

> D2 Receptor Antagonists

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8
Q

Outline the features of 5HT receptor Antagonists
> Examples
> Mechanism of Action when acting on Visceral Afferents
> When is it used
> Side Effects

A

Examples:
> OndanSETRON
> GraneSETRON

MOA:
> Peripherally reduced gut mobility and GI Secretion
> Centrally - Acts to inhibit the CTZ

When is it used:
> First line of treatment typically

Side effects:
> Constipation 
> Headache 
> Elevated LFTs
> Long QT syndrome 
> Extra Pyramidal effects - Dystonia, Parkinsonism
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9
Q 
Outline the features of Dopamine (D2) Receptor antagonists:
> Examples x2 
> MOA when acting on Visceral Afferents 
> When is it used
> Side Effects
A

Examples:
> Metoclopramide
> Domperidone

MOA:
> Both similar 
> Increases Acetylcholine at muscarinic receptors in the gut 
- Promotes Gastric empyting
- Increases tone at LOS so it closes 
- Increases tone and amplitude of gastric contractions 
- decrease tone of pylorus so it opens 
- Increases peristalsis 
When is it used 
> Metoclopramide 
- GORD
- Ileus 
> Domperidone 
- improving lactation and breastfeeding in mothers

Side Effects
> Glactorrhoea via prolactin release
> Extra pyramidal effects
> Sudden cardiac death (D2)

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10
Q

What agents act on the CTZ ?

A 
> 5HT3 receptor Antagonists 
> H1 Receptor Antagonists 
> Muscarinic Receptor Antagonists 
> D2 Receptor Antagonists 
> Corticosteroids 
> Cannabinoids
> NK1 Receptor Antagonists
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11
Q

Give examples on D2 Receptor Antagonists which work on the CTZ.
> When are they used ?

A
  • ProchlorperaZINE
  • LevomepromaZINE
  • Haloperidol
When is it used 
> ZINEs
- Motion sickness 
- Vertigo
- Prochlorperazine good for pregnancy 
> Haloperidol 
- Chemotherapy 
- Palliation
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12
Q

Outline the features of Corticosteroids acting on the CTZ:
> Examples
> when are they used
> Side Effects

A

Examples:
> Dexamethasone
> Methylprednisolone

When are they used ?
> Perioperative N+V
> Chemotherapy

Side Effects:
> Insomina
> Increased appetite
> Increase blood sugar

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13
Q

Outline the features of Cannbinoids acting on the CTZ:
> Examples
> When is it used
> Side Effects

A

Examples
> Nabilone

When is it used
> Last line Chemotherapy

Side Effects
> Dizziness
> Drowsiness

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14
Q 
Outline the features of NK1 Receptor antagonists acting on the CTZ 
> Examples 
> MOA
> When is it used 
> Side effects
A

Examples
> AprePITANT

MOA:
> Prevent action of substance P at CTZ and in peripheral nerves
> Boost effects of 5HT3 RAs
> Anxiolytic and anti depressant properties

When is it used:
> Chemotherapy especially delayed emesis

Side effects:
> Headaches
> Diarrhoea / Constipation
> Steven Johnson syndrome

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15
Q

When would not use D2 Receptor Antagonists ?

A

They are prokinetics so don’t use if there is an obstruction or you risk perforation

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16
Q

List some triggers of the CTZ

A 
> Hormones - BHcG in pregnancy 
> Drugs 
- Chemotherapy 
- Anaesthetics 
- Opiates
17
Q

What is Hyperemesis Gravidarum

  • Problems
  • Treatment
A

Rapid rise in BHcG stimulates the CTZ
- More than just morning sickness

Problems:
> Dehydration 
> Weight Loss
> Electrolyte Imbalance 
> Urinary Ketones

Treatment:
> Promethazine / Prochlorperazine
> Metoclopramide
> Ondansetron

18
Q

Outline the treatment for chemotherapy related emesis

A

1) Corticosteroid - Dexamethasone
2) 5HT3 RA - Ondansetron
3) NK1 Antagonists - Aprepitant
Add with relative risk
For rescue give Metoclopramide - D2 RA

19
Q

What are the risk factors for Post operative N+V

A 
Patient:
> Younger Age 
> Previous history of PONV 
> Non smoker 
> Female

Anaesthetic:
> General > Regional
> Volatile anaesthetic gases
> Post Operative Opioids

Surgery:
> Duration of Operation
> Laproscopic

20
Q

How is PONV prevented ?

A

Depending on the risk:

  • Low => Wait and see
  • Moderate => 1/2 Antiemetic agents
  • High => > 2

If prophylaxis fails add antiemetic from another class

21
Q

What 3 ways can diarrhoea be treated ?

A

> Increase transit time of poo through the gut allowing for better nutrition and rehydration
Comfort
Prevent Incontinence

22
Q

Outline the features of Opioid Receptor Antagonists on treating Diarrhoea:
> Examples
> MOA
> Side Effects

A

Examples;
> Loperamide
> Codeine
> Morphine

MOA:
> Specific to u receptors in the myenteric plexus
- Decreases tone of longitudinal and circular smooth muscle
decreases colonic mass movement by supressing gastrocolic reflex

Side effects:
> Paralytic Ileus
> N+V
> Sedation and Addiction

23
Q

What lifestyle changes can be made to help prevent diarrhoea ?

A

Typically for people with long term loose stools
> Bananas - High K+ and fibre
> White Rice - Binds Stool
> Pasta - Low in fibre
> Limit to 3 fruit portions / day
> Avoid caffeine, sorbitol, fatty / spicy foods and fizzy drinks
> Consider probiotics

24
Q

What lifestyle changes can be made to prevent constipation ?

A

> Drink more water
Increase fibre intake
Regular exercise
Toilet routine

25
Q

What different types of laxatives are there to treat constipation:
> Examples
> MOA

A

Osmotic Laxatives - Lactulose , Movicol
> Draw fluid in
> Retain fluid they came with (Macrogols)

Stimulant - Bisacodyl , Glycerin
> Increase intestinal mobility
> Glycerin is also a stool softener

Bulk Forming - Ispaghula Husk
> Medicinal fibre

Stool Softeners - Docusate sodium , Glycerin suppository
> Decrease surface tension of stool
> Increase penetration of fluid into stool

Pharmacology (25 decks)

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