Antiemetics Flashcards
What is emesis?
Involuntary,forceful expulsion of gastric contents through the mouth
Process of vomiting
- coordinated by vomiting centre in medulla
- take a deep breath
- glottis closes
- abdominal muscles contract
- lower oesophageal sphincter relaxes
- retrograde peristalsis of small bowels
What is vomiting coordinated by?
Vomiting centre in medulla
Neurological pathway of vomiting
- When the vomiting centre in the medulla is stimulated the vomiting reflex occurs
- motion + morning sickness trigger the vestibular centre > CTZ > vomiting centre
- cytotoxic agents trigger the CTZ > vomiting centre
- high cortical centre in brain can be triggered by pain, emotion or repulsive sights/smells > vomiting centre
What receptors are found in the vomiting centre
- NK1
- Muscarinic Ach
- H1 - histamine
- 5HT2 - serotonin receptor
Stimuli for the higher cortical centre of nausea
- Pain
- Repulsive sights + smells
- Emotional factors e.g. stress
Management of nausea due to stimuli from higher cortical centre
Conservative management - avoid stimulus
What portion of the brain is involved in motion sickness?
Vestibular nuclei
Due to inputs from the labyrinth centre
Act on NK1, Muscarinic Ach, H1 + 5HT2
What receptors are in the vestibular nuceli?
Muscarinic Ach
H1
What receptor is in the higher cortical centres?
GABA
Example of Muscarinic antagonists
Hyoscine hydrobromide
What is the mechanism of action of Muscarinic antagonists?
Competitive blockage of Muscarinic acetylcholine receptors - act on vestibular nuclei
What are adverse drug reactions of muscarinic antagonists?
Sedation
Consiptiaon
Dizziness
Dry mouth
Visual problems
Confusion
What are contraindications of muscarinic antagonists?
Elderly patients
Glaucoma
What are important drug drug interactions of Muscarinic antagonists?
Anti-psychotic meds
Examples of H1 antagonists
Cycilzine
Levomepromazine
Prochlorperazine
Promethazine
What are uses of H1 antagonist?
Motion sickness
Promethazine - morning sickness in pregnancy
What is the mechanism of action of H1 antagonists in treatment of vomiting?
- Works centrally
- Acts on vomiting centre + vestibular nuclei
- inhibits histaminergic signals from vestibular system to CTZ in medulla
What are adverse drug reactions of H1 antagonists?
Sedation
Dry mouth
Constipation
Urinary retention
Blurred vision
What are contraindications of H1 antagonists?
Epilepsy
Urinary retention
Children + elderly
Glaucoma
Who is motion sickness more common?
Women
Children
People who have migraines
Prevention of motion sickness
Hydration
Position in vehicle
Distraction
What 2 classes of drugs are used in the treatment of motion sickness?/
Examples of each
- Anti muscarinics e.g. hyoscine hydrobromide
- anti histamines e.g. cyclizine, propchlorperazine
What affects the chemotherapy trigger zone?
- inputs from vestibular centre
- cytotoxic agents e.g. chemotherapy
- vagal afferents
What are the receptors of the chemotherapy trigger zone?
NK1
D2 - dopamine
5HT3 - serotonin