What triggers the chemoreceptor trigger zone? what drugs are used?
Drugs: chemo, opioid, anaesthetic
Chemicals
Toxins
- 5HT antagonist
- Neurokinin receptor antagonist
- Antimuscarinic
- Antihistamine
What triggers the GI tract? what drugs are used?
Chemotherapy
Operation
Radiotherapy
Food poisoning
- Dopamine receptor antagonist (prokinetic)
- 5HT antagonist
What triggers the cortisol centre? What drugs are used?
Sensory input: pain, sight, smells
Emotions
Anticipatory
- Benzodiazepine
- Cannabiniod
What triggers the vestibular system? What drugs are used?
Motion sickness
Labyrinth disorder: vertigo
- Antihistamine
- Antimuscarinic
What is the treatment for nausea and vomiting in pregnancy?
First line: rest, hydration + change diet
Persistent
- Antiemetic: Metoclopramide, Prochlorperazine, Cyclizine, Promethazine (sedating), Ondansetron
- 24h symptoms: switch to diff class
- 48h: seek specialist opinion
What is the treatment for post-operative nausea + vomiting?
Before a patient has an operation, they are assessed on their risk of nausea and vomiting, If at high risk, offer prevention with a combination of two or more anti emetics from different drug classes:
- Metoclopramide
- Domperidone
- Dexamethasone
- Prochlorperazine , droperidol, haloperidol
- Cyclizine
What is classed as high risk post-operative nausea and vomiting?
- Female
- Non-smoker
- Hx motion sickness
- Opioid
- Anaesthetic
- Surgery type + duration
Give examples of dopamine receptor antagonist used in N+V
- Domperidone (choice in PD)
- Metoclopramide
Give examples of 1st gen antipsychotics used in N+V
- Prochloperazine (bucally: migraine)
- Levopromazine (palliative)
- Droperidol (post-op)
- Haloperidol (palliative)
Give an example of a 5HT receptor antagonist used in N+V
Ondansetron
Give an example of an antimuscarinic used in N+V
Hyoscine hydrobromide (most effective. Motion sickness)
What is the mechanism of action of metoclopramide?
- Blocks D2 receptors in chemoreceptor trigger zone
- Acts directly on GI tract = prokinetic effect
- It promotes gastric emptying and increases gastrointestinal motility
What is the indication of metoclopramide?
- Nausea + vomiting
- Prevention: post op, chemo + radiotherapy
What is the dose of metoclopramide?
10mg TDS 5 days
- 18+
- Max: 500mcg/Kg
What is the side effect of metoclopramide?
Acute dystonic reactions: oculogyric crises
- Uncontrolled muscle spasms in the face, skeletal muscles and eyes
- Common in young females and the elderly
- MHRA: neurological effects - restricted use
What are the interactions of metoclopramide?
- Antipsychotics → INC extrapyramidal symptoms
- Dopaminergic drugs + PD → Do not give, antagonises treatment + worsens condition
What is the mechanism of action of domperidone?
- Blocks D2/D3 receptors in chemoreceptor trigger zone
- Acts directly on GI tract = prokinetic effect
- It promotes gastric emptying and increases gastrointestinal motility
What is the indications of domperidone?
Nausea + vomiting
Choice in PD
What is the dose for domperidone?
10mg TDS 1 week
- Over 35kg
- MHRA: domperidone: lack of efficacy in certain populations (Under 12 + <35kg)
What are the side effects of domperidone?
QT prolongation
CI:
- Impaired cardiac conduction
- Cardiac disease
- Avoid in mod-severe hepatic impairment
What are the interactions of domperidone?
QT prolongation = arrhythmias
- Antipsychotics
- Antiarrhythmics
- Escitalopram + citalopram
- Macrolides
CYP3A4 inhibitor
- Amiodarone
- Azole
- Macrolides
- Rate limiting CCBs
What is the mechanism of action of 5 HT3 receptor antagonists?
Blocks 5-HT3 receptors in chemoreceptor trigger zone + GI tract
What is the indication for 5-HT3 receptor antagonists?
Post operative + chemotherapy induced nausea + vomiting
What are the side effects of 5-HT3 receptor antagonists?
QT prolongation
