8.3- Anti-Emetics Flashcards
What is vomiting ( emesis)? Give a definition
- Physiologic response to irritating and potentially harmful substances in blood or gut
- Can also be due to
- Excessive vestibular stimulation
- Psychological stimuli
How does vomiting occur physiologically?
- Coordinated contractions of pharyngeal, GI, abdominal wall
- Coordinated in the vomiting centre
Where is the vomiting centre located?
What is the vomiting centre influenced by? ( ie triggers)
Located in the medulla
Triggered by:
- Vestibular apparatus in inner ear
- Chemoreceptor Trigger Zone ( CTZ) in medulla
- Solitary Tract; collection of nerve fibres in the medulla
Name the two vagal afferent triggers to the vomiting centre
and name the one vagal efferent location
Vagal AFFERENTS:
- Solitary tract
- Chemoreceptor Trigger Zone ( CTZ)
VAGAL EFFERENT; The Gut
Which of the triggers are positive and negative?
Positive;
Cerebral cortex ( but CAN BE NEGATIVE )
Solitary tract
Vestibular apparatus
CTZ
Name the 6 classes of anti-emetics
- Dopamine inhibitors
- Serotonin inhibitors
- Anti-histamines
- PHENOTHIAZINE
- Anti-cholinergics ( less common)
- Neurokinin 1 inhibitors ( less common)
Give 2 examples of Dopamine inhibitors
- Metoclopramide
- Domperidone ( think of the champagne lol)
Describe the mechanism of action of dopamine inhibitors
- Binds to receptors to inhibit the action of dopamine
- mainly in the CTZ in the medulla, which is rich in D2 receptors
- Prokinetic effect in the GI
Name the two sites of action of dopamine inhibitors
- Chemoreceptor Trigger Zone ( CTZ)
- Solitary tract
bind to D2 receptors
Name 2 side effects and 2 contraindications for the use of dopamine inhibitors
Side effects;
- Diarrhoea; because of prokinetic effect in the GI
- Metoclopramide has extrapyramidal side effects eg dyskinesia, Parkinsonism, dystonias
Contraindications;
- GI obstruction
- GI perforation
Describe the mechanism of action of serotonin inhibitors and give an example of one
e.g. ONDANSETRON
Mechanism of Action:
- Binds to receptors to inhibit action of serotonin
- mainly in the CTZ which is rich in 5-HT3 receptors
- (Normally, serotonin is released by the gut in response to emetogenic/ nausea propagating stimuli)
ACTS on 5-HT3 receptors in Solitary Tract, Gut and CTZ
Give 3 side effects of serotonin inhibitors
Give 1 contradindication for use of Serotonin inhibitor
What type of disease-caused nausea is it known to cause?
Side effects:
- constipation
- diarrhoea
- headache
CONTRAINDICATION: risk of QT prolongation if it is used with SSRI’s, antipsychotics
Commonly used to alleviate CHEMOTHERAPY-INDUCED NAUSEA
Give 2 examples of anti-histamines
and
2 sites of action
e.g.
- Cyclizine ( main one)
- Promethazine
SITES:
- Solitary tract
- Vestibular apparatus
Describe the mechanism of action of anti-histamines
Give 2 side effects
Give 2 contraindications
blocks H1, M1 receptors between vestibular system and vomiting centre
SIDE EFFECTS:
- drowsiness
- Anti-cholinergic effects
CONTRAINDICATIONS:
- prostatic hypertrophy
- Hepatic encephalopathy
Give 2 examples of PHENOTHIAZINES
What are the 3 sites of action
- prochlorperazine
- chlorpromazine
SITES OF ACTION:
- Vestibular apparatus
- Solitary Tract
- CTZ
What is the mechanism of action of phenothiazines?
- Blocks D2 receptor in CTZ, gut
- To a lesser extent, blocks H1, M1 receptors in CTZ, vestibular apparatus
Give 4 side effects of Phenothiazines
Give one contraindication of phenothiazines
SIDE EFFECTS:
- Drowsiness
- Postural hypotension
- Extrapyramidal side effects
- Anti-cholinergic side effects
CONTRA: Risk of QT prolongation; avoid with quinine, SSRI’s, anti-psychotics
Give an example of an anti-cholinergic and describe its MOA
Describe their MOA
Give its side effects and contraindications
e. g.
* Hyoscine hydrobromide
BLOCKS M1 receptors
SIDE EFFECTS: Anti-cholinergic side effects
Conta: GI OBSTRUCTION
What woud you use for Hyperemesis Gravidarum ( GE) ie profuse pregancy vomiting?
SHORT TERM; Antihistamine e.g. CYCLIZINE
followed by
- Phenothiazine
- Dopamine inhibitor
What factors could cause vomiting post-op?
- anaesthetic
- type and duration of surgery
- female
- non-smoker
- intra-operative opioid use
What anti-emetics would you prescribe post-op?
- Serotonin inhibitors
- Phenothiazine
- Anti-histamine
What anti-emetics would you prescribe for each of the following:
a) Chemotherapy
b) Motion sickness ( hint; caused by the vestibular apparatus)
c) Opioid induced
a) CHEMO- serotonin inhibitor
b) Motion sickness- antihistamine ( acts MAINLY in vestibular apparatus on H1, M1 receptors)
c) Opioid induced nausea- DOPAMINE Inhibitors
