Anti-Emetics Flashcards
What stimulates Nausea and vomiting?
- Toxins: Bacterial poisons, alcohol (15%)
- Smells
- Motion sickness
- Migraine
- Pregnancy
- Drugs
What is the physiological response of Vomiting and Nausea?
- Discomfort, dry mouh, salivary inhibition
- Yawning-sympathetic distress
- Reappearence of saliva
- Pylorus closes
- Tone of stomach increase
- Deep breath
- Contraction of abdominal muscle to force out food
- Forced expiration to prev inhalation
What NT are involved in Nausea and vomiting?
- Histamine
- Acetylcholine
- Dopamine
- 5-HT
- Neurokinin
- Blocking these receptors in the brain prevents nausea and vomiting
What is the vomit centre of the brain?
- Located within medulla
- Recieves afferent signals from vagus nerve and CTZ
What receptors are important for vomiting?
- 3 receptors abundant in the chemoreceptor trigger zone (CTZ)
- BLocking these is important for prev vomiting
- D2
- 5-HT3
- NK-1
What are the 4 main pathways?
- Chemoreceptor trigger zone (CTZ)
- Vagal afferent nerve fibres from GIT
- Central vestibular nuclei
- Higher centres of brain
What is the chemoreceptor zone(CTZ)?
- Outside BBB
- REceptors 5-HT3, D2 and NK1 (substance P)
What is motion sickness?
- Afferents from inner ear (vestibulo-cochlear system) feed into vomiting centre
- Mediated by acetlycholine and histamine
- Inner ear infections can also cause motion sickness
How does chemotherapy induce nausea?
- Some chemotherapy agents stimulate release of 5-HT from enterochromaffin cells in GIT
What are Histamine H1 receptor antagonists work?
- Motion sickness
- Morning sickness of pregnancy
- Space motion sickness
- Anti-muscarininc actions
- Produce drowsiness and sedation
(Block receptor in Vestibular nuclei see PP)
What are Muscarinic M1 receptor antagonists?
- Prophylaxis and treatment of motion sickness
- Also reduce gastic motility
- Anti-muscarinic side effects
- Produce drowsiness
- Naturally occuring foundin Atropa belladona
- Block receptor in Vestibular nuclei (See pp)
What is the Reflex mechanism of vomiting?
- Central regulation of vomiting occurs in the vomiting cntre and the CTZ
(CTZ sensitive to chemical stimuli–main site of anti-emetics) - Output from CTZ stimulates the vomiting centre, leading to initiation of vomitin
- Neuronal signals from GI tract feed into CTZ and vomiting centre
What is the Vomiting protective reflex?
- Chemoreceptors in GIT activated by toxins–
- effect vagal nerves–
- feed into nucleus tractus solitarius and in turn, vomiting centre
What are Dopamine D2 receptor antagonists?
- Act in CTZ but has unwanted CNS effects
- D2 receptor inv in movt
- Antagonism leads to parkinson’s like symptoms
- Effective against chemotherapy-induced emesis
- Also stimulates gastric emptying and reduce nausea
- Works in CTZ on D2 receptor
What are 5-HT receptor antagonists?
- Blocks 5-HT at 5-HT3 receptors in gut and CNS
- Particularly effective against chemotherapy-induced emesis
- Not effective for motion sickness
- Work in GIT and CTZ (See pp)
What are Neurokinin (NK1) receptor antagonists?
- NK1 receptor activated by substance P
- NK1 receptor antagonists suppress nausea and vomiting
- Used in chemotherapy-inuced N&V in combo with 5-HT receptor antagonist
- Work on NK1 receptors in CTZ an GIT
What are seroids used for in N&V?
- Used in chemotherapy-induced N&V
- Mechanism unknown
What is Apomprohine?
- Metabolite of morphine
- No effect on opiod receptors
- Non-selective dopamine receptor agonist
- Used as emetic in veterinary medicine
- Also used to treat Parkinson’s disease
Summarise N&V.
- N&V regulated by CNS
- Response to signals from periphery
- Number of NTs involved
- Chemotherapy-induced N&V controlled using 5-HT3 and NK1 receptor antagonist along with a steroid
