Pharmacology of Nausea and Vomiting Flashcards
Vomiting/nausea may be caused by?
Anxiety
Motion sickness
Pregnancy
Side effects of drugs
What is nausea?
Unpleasant urge to vomit
What is vomiting and it’s medical name?
Emesis
Forceful expulsion of stomach contents
Defence mechanism triggered by emetic centre in brain stem
Retching?
Repetitive reverse peristalsis
What is regurgutation?
Effortless movement of food contents
Stomach acid coming back into the mouth
Pathway of vomiting?
Systemic toxins in gut lumen
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Enterochromaffin cells in mucosa release mediators like 5HT
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Depolarisation of sensory afferent terminals in mucosa (5HT3 receptors)
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AP discharge in vagal afferents to brainstem
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Coordination of vomiting by vomiting centre
What is the vomiting centre?
Group of interconnected neurones within medulla
What are the events of vomiting?
- Sphincters are relaxed
- Retrograde contractions from ileum to stomach take place
- Preceeded by salivation, sweating, elevated HR and aspiration
Where is the CTZ and what is it?
Chemoreceptor trigger zone
located next to vomiting centre (medulla) - opposite side of brain barrier from VC
What is the chemoreceptor trigger zone triggered by?
Cancer chemotherapy opiods+ chemo & radiotherapy gastroenteritis
What acts on the CTZ?
DA antagonists
5HT3 antagonist
What is the VC?
Vomiting centre
What is the VN?
Vestibular nuclei
What does VN do?
Acts on VC in motion sickness
What drugs act on the VN?
H1 antagonist
Anti-muscarinic drugs
Examples of anti-emetics?
Antihistamines 5HT3 receptor antagonists Dopamine Receptor Antagonists Neurokinin- 1 Receptor Antagonists Metoclopramide
Examples of anti-histamines?
Antagonists at histamine H1 receptors in brain (blocks H1 receptors in VN)
What are antihistamiines useful for?
Motion sickness
Side effects of antihistamines?
Sedation
What do antimuscarinics do?
Act as antagonists at muscarinic ACh M1 receptors in brain ( block muscarinic receptors in VN and VC)
What are antimuscarinics used for?
Motion sickness
Examples of anti-muscarinic drugs?
Scopolamine (hyoscine)
Side effects of anti-muscarinic drugs?
Dry mouth
Tachycardia
Constipation
Examples of 5HT3 receptor antagonists?
Granisetron
Ondansetron
Palonosetron
What do 5HT3 receptor antagonists do?
Block 5HT3 receptors in the GIT and CNS
What are 5HT3 receptor antagonists used for?
Good for chemo induced nausea & vomiting
Radiation induced emesis
Post-operative nausea/vomiting
Side effects of 5HT3 receptor antagonists?
Constipation
Diarrhoea
Headache
Examples of dopamine Receptor antagonists? (DA)
Prochloroperazine Droperidol Haloperidol Trifluoperazine Chloropromazine Metoclopramide
What do Dopamine receptor antagonists do?
Block D2 receptors in the CTN of he medulla and D2 receptors in the GIT
What are Dopamine receptor antagonists used for?
Nausea & vomiting associated with neoplastic disease
Radiation sickness
Drug-induced emesis
Side effects of Dopamine receptor antagonists?
Diarrhoea
Extrapyramidal side effects
Examples of Neurokinin 1 receptor Antagonists?
Fosaprepitant
Aprepitant
How do Neurokinin 1 receptor antagonists work?
Block NK1 receptors in GI tract and the CTZ of medulla in hindbrain- blocking side effects of substance P (which evokes vomiting)
Side effects of Neurokinin receptor antagonists?
Constipation
Headache
Examples of anti-diarrhoeal drugs?
Loperamide
Diphenoxylate
What are anti-diarrhoeal drugs?
Electrolyte replacements
Side effects of anti-diarrhoeal drugs?
Constipation
Sedation
Respiratory depression