Nausea, vomiting and diarrhoea Flashcards
What actually happens in vomiting?
- Co-ordinated by the vomiting centre in the medulla
- Take a deep breath
- Glottis closes
- Abdominal muscles contract
- Lower oesophageal sphincter relaxes
- Retrograde peristalsis of small bowels
What are the inputs to the vomiting centre?
- Higher cortical centres - pain, repulsive sights and smells, emotional factors
- CTZ - main site for sensing emetic stimuli (receives input from the vestibular nuclei)
- Vagal afferents convey signals from gut to brainstem
What do we target to treat motion sickness?
- Muscarinic ACh receptors
- H1
Give some examples of muscarinic antagonist drugs?
- Hyoscine hydrobromide
What is the mechanism of action of muscarinic antagonists?
- Competitive blockade of muscarinic acetylcholine receptors
What are the adverse side effects of anti-muscarinics?
- Sedation
- Constipation
- Dizziness
- Dry mouth
- Visual problems
- Confusion
What are the contraindications of anti-muscarinic drugs?
- Elderly patients
- Glaucoma
What are the DDIs of anti-muscarinic drugs?
- Anti-psychotic medication
Give some examples of H1 antagonists?
- Cyclizine
- Levomepromazine
- Prochlorperazine
How do H1 antagonists work?
- Works centrally
- Acts on the vomiting centre and vestibular nuclei
- Inhibits histaminergic signals from the vestibular system to the CTZ in the medulla
What are the adverse side effects of H1 antagonists?
- Sedation
- Anti-muscarinic side effects e.g. dry mouth, constipation, urinary retention, blurred vision
What are the contraindications of H1 antagonists?
- Epilepsy
- Glaucoma
- Urinary retention
- Children
- Elderly patients
Which H1 antagonists are sedating?
- Diphenhydramine (Benadryl)
- Promethazine
- Chlorphenamine
- Cinnarizine
- Cyclizine
Which H1 antagonists are non sedating?
- Cetirizine
- Fexofenadine
- Loratidine
Outline the epidemiology of motion sickness?
- Very common
- Affects women more than men
- Affects children more than adults
- People who have migraine
What are the practical methods of motion sickness prevention?
- Hydration
- Position in the vehicle
- Distraction
What are the drugs used to treat motion sickness?
- Anti-muscarinics - hyoscine (scopolamine)
- Anti-histamines - cinnarizine, cyclizine, prochlorperazine
Which drugs can make a patient feel nauseous?
- Chemotherapy
- Opioids
- General anaesthetics
- Digoxin
- NSAIDs
- Diuretics
- Antibiotics
Which metabolites can cause nausea?
- Uraemia
- DKA
- Addison’s disease
- Hyperthyroidism
Which toxins can cause nausea?
- Bacteria
- Viral
Give some examples of D2 receptor antagonists
- Metoclopramide
- Domperidone
- Haloperidol
- Prochlorperazine
Outline the mechanism of action of metoclopramide
- Central dopamine antagonist
- Peripheral cholinergic agonist
- Increases acetylcholine at muscarinic receptors in the gut
- Promotes gastric emptying
- Increases tone at lower oesophageal sphincter
- Increases tone and amplitude of gastric contractions
- Decreases tone of pylorus so it opens
- Increases peristalsis
What are the adverse side effects of metoclopramide?
- Depression
- Diarrhoea
- Drowsiness
- Hypotension
- Galactorrhoea
- Extra-pyramidal effects e.g. dystonia, parkinsonism
What are the contraindications of metoclopramide?
- Post-GI surgery
- GI obstruction
- GI perforation
- GI haemorrhage
How does domperidone work?
- Similar mechanism to metoclopramide
- Good for improving lactation in breastfeeding mothers
Why is domperidone not used as frequently anymore?
- Increased risk of cardiac side effects
What are the adverse side effects of domperidone?
- Dry mouth
- Long QT interval
- Ventricular tachycardia
- Galactorrhoea
- Loss of libido
What are the contraindications of domperidone?
- Patients >60 years old
What is the mechanism of action of haloperidol?
- Act on the CTZ
What are the adverse side effects of haloperidol?
- Parkinsonism
- Movement disorder
- Long QT
- Arrhythmia
- Constipation
- Dry mouth
What are the contraindications of haloperidol?
- Parkinson’s disease
- Cardiovascular disease
- Diabetes
- Myasthenia gravis