Nausea and Vomiting NOTFINISH Flashcards
What are the 5 main causes of nausea and vomiting?
- Gastrointestinal
- Chemical irritation
- Vestibular
- CNS
- Prengnacy
Give an example for chemical irritation based cause of nausea and vomiting
Radiotherapy, drugs and toxins
Give an example for a CNS based cause of nausea and vomiting
Anxiety, raised intracranial pressure
What are the four sources of afferent input for the vomiting centre
- Chemoreceptor trigger zone (CTZ)
- Vestibular system
- Vagal and spinal nerves from GI tract
- CNS
What triggers the chemoreceptor trigger zone to send signals to the vomiting centre?
Stimuli from the blood or CSF - e.g. drugs or toxins
What triggers the vestibular system to send signals to the vomiting centre?
Motion sickness
Muscarinic and histamine receptor activation
What triggers the vagal and spinal nerves of the GI tract to send signals to the vomiting centre?
Irritation of the mucosa causes release of serotonin by enterochromaffin cells.
5-HT3 receptors send signals.
What do enterochromaffin cells release?
They release serotonin on irritation to the gut mucosa.
What is the action of metoclopramide?
Enhances response to acetylcholine in GI tract
- Slows down peristalsis
Blocks dopamine receptors in CTZ
- Preventing vomiting reflex
What are the side effects of dopamine blockers?
Extrapyramidal symptoms (movement-based effects)
Also, those that do cross the BBB cannot be used in Parkinson’s
What type of drug CANNOT be used in patients with Parkinson’s Disease?
Dopamine blockers.
(Unless they do not cross the BBB - Domperidone)
What are the three dopamine antagonists used in nausea and vomiting management?
Metoclopramide
Prochlorperzaine
Domperidone
What is the action of prochlorperazine?
Anti-emetic effects due to dopamine antagonism (blocks CTZ vom reflex) and muscarinic receptor antagonism (slows peristalsis)
What is the action of domperidone?
Dopamine antagonist that DOESNT cross teh BBB.
Blocks dopamine receptors in upper GI tract, resulting in increased motility
Orally administered, and safe to use in Parkinsons.
How are 5HT3 antagonists named, giving two examples
Name ends in -setron
E.g. Ondansetron, Palonosetron
What is the major and minor effect of 5HT3 antagonists?
For what causes of vomiting are they useful / not useful?
Major effect = block serotonin in upper GI tract
Minor effect = block vomiting centre and CTZ
5HT3 antagonists are most useful for causes mediated through irritation of the GI tract (major effect), not at all useful for nausea caused by other mechanisms, such as motion sickness through vestibular or CNS-mediated nausea.
How are steroids used in management of nausea/vomiting
Dexamethazone is a glucocorticoid used in chemotherapy and peri-operative settings.
Reduce peri-tumoural oedema in cases of raised intracranial pressure secondary to brain tumour. Higher pressure results in nausea.
What are the short and long term side effects of using glucocorticoids to manage nausea in raised intra-cranial pressure?
Short term - increased blood sugar, hunger, HTN
Long term - osteoporosis, diabetes mellitus
What is the action of aprepitant?
Aprepitant is a neurokinin (NK-1) receptor antagonist
It blocks the effect of substance P, preventing emetic signals from being transmitted.
It crosses the BBB.
What is fosaprepitant?
Fosaprepitant is the IV prodrug of aprepitant.
It is metabolised to aprepitant with a half life of two minutes - very rapid.
Aprepitant is otherwise adminstered orally.
What is the action of the Hyoscine group of drugs?
Anticholinergic drugs at muscarinic receptors, also have minor histamine and serotonin antagonism
What is the difference between Buscopan and Kwells? (Hyoscine drugs)
Buscopan = hyoscine butylbromide
Used to relieve stomach and bladder cramps/spasms. Not an effetive antiemetic
Kwells = hyoscine hydrobromide
Crosses the BBB - an effective antiemetic.
What is the action of cyclizine?
Histamine antagonist, with main action at the CTZ.
Useful when the histamine pathway is involved e.g. in motion sickness, bran metastasis
What is the action of lorazepam?
Very potent benzodiazepine, binds to CNS.
Used in anticipatory nausea associated with chemotherapy.
As it is a benzodiazepine, involved sedation as a side effect.
Which drugs are safe to use in pregnancy to manage nausea/vomiting?
Cat A drugs = lots of human experience that it is not harmful
Examples: Metoclopramide, Pyridoxine
What is the mainstay of treatment for children with nausea/vomiting?
Key focus is rehydration, avoiding mediations.
This is due to high rate of extrapyramidal symptoms from dopamine antagonism.
