Anti-Emetics Flashcards
State the 4 major classes of anti-emetic drugs.
H1 receptors
Dopamine (D2) receptor antagonists
Muscarinic receptor antagonists
Serotonin (5-HT3) receptor antagonists
What types of receptors in the stomach transmit signals to the vomiting centre and chemoreceptor trigger zone?
Chemoreceptors and Mechanoreceptors
What is special about the location of the CTZ and vomiting centre?
It is located in a part of the brain that has a very porous blood brain barrier
So the CTZ and vomiting centre act as an early warning system to protect the brain from toxin damage
What are the uses of promethazine?
Motion sickness
Give of example of dopamine receptor antagonists.
Metoclopramide
Give an example of a muscarinic receptor antagonist.
Hyoscine
What is the mode of action of muscarinic receptor antagonists in anti-emetics?
Act centrally on the CTZ, vestibular nuclei and vomiting centre to block the activation of the vomiting centre
What is hyoscine used for?
Prevention of MOTION SICKNESS
Give an example of a serotonin receptor antagonist.
Ondansetron
What is the mode of action of serotonin receptor antagonists?
Act to block transmission in visceral afferents and CTZ
What is the main use of serotonin receptor antagonists as an anti-emetic?
MAIN USE: preventing anti-cancer drug induced vomiting (especially cisplatin)
Example of treatment that can cause vomiting
Cisplatin for lung cancer-chemotherapy induced nausea and vomiting
Pathophysiology of cisplatin
Toxic to ECL cells in the stomach which cause release of free radicals. These free radicals cause an excessive serotonin release. The serotonin activates 5-HT3A receptors on nerve fibres to Chemoreceptor Trigger Zone
Effect of activation of CTZ
Activates fibres to vomiting centre which induces feeling of vomiting
Combined therapy for CINV
Ondensatron- 5HT3A antagonist
Glucocorticoids- reduce free radicals
Aprepitant- neurokinin 1 therapy
Common presentation of afro-carribean person for vomiting
Motion sickness
Pathophysiology of motion sickness
Neural mismatch in the labyrinth which activates histamine receptors on vestibular nuclei. Vestibular nerve fibres then activate muscarinic receptoes on CTZ which activates muscarininc receptors in VC
Treatment for motion sickness
Promethazine
Hyoscine
What is promethazine
H1 receptor antagonist
Pathophysiology of gastroparesis
Delayed emptying of the stomach and reduced stomach contraction.
How does gastroparesis cause vomiting
Get an increase in 5-HT that activates 5-HT3A receptors on CTZ-> this activates muscarinic fibres on VC
Treatment of gastroparesis
Metoclopramide
What does metoclopramide do
D2 receptor antagonist
5-HT3A receptor antagonist - acts on CTZ
How is a dopamine 2 receptor antagonist useful in vomiting treatment
Stimulates gastric opening
Inhibits D2 receptors in CTZ
Where does CTZ recieve inputs from
Stomach
Vestibular nuclei
Receptors associated with CTZ
Serotonin- 5HT3A
Muscarinc 1-2
Dopamine 2
Receptor associated with vestibular nuclei
Histamine
Receptor associated with VC
Muscarinic
Main causes of vomiting
Cytotoxic drugs Motion sickness Pregnancy GI problems Parkinsons treatment due to dopamine
Side effects of muscarinic antagonists
Drowsiness
Dry mouth
Side effects of H1 antagonist
Drowsiness
Side effects of D2 receptor antagonists
Extra-pyramidal effects
Galactorrhoea
Side effects of serotonin antagonists
Headaches
Constipation
