Antiemetic drugs - Ch. 84 Flashcards
What are antiemetic drugs used for?
Used to relieve nausea and vomiting
-More difficult to control nausea
What are the brain regions responsible for vomiting?
Vomiting centre (VC) -coordinates muscles
Chemoreceptor trigger zone (CTZ) -leads to reflex
-Both in the medulla oblongata
What neurotransmitters are involved in the vomitting reflex?
Histamine (H1 receptors)
ACh (muscarinic receptors)
5-HT (5-HT3 receptors)
Dopamine (DA2 receptors)
Substance P (neurokinin 1 receptors)
What are some causes of N&V that antiemetics are used for?
Cancer chemotherapy-induced (CINV)
Post op with general anesthesia
motion sickness
What is the mechanism of action of 5-HT (serotonin) antagonist antiemetics?
Block 5-HT3 (serotonin) receptors in CTZ and VC and GI
Examples of 5-HT (serotonin) antagonists?
Odansetron
Dolasetron
Granisetron
Palonosetron
What types of N&V are 5-HT (serotonin) antagonists used for?
CINV
Post op N and V
What is the mechanism of action of dopamine (DA) receptor antagonists?
Block DA receptors in the CTZ
What type of N&V is DA receptor antagonists used for?
Severe vomiting
e.g, CINV, radiation therapy
What are the other indications that DA receptor antagonists are used for?
Antipsychotic (neuroleptic) agents
Prokinetic agents (increase GI motility)
Examples of DA receptor antangonists?
Chlorpromazine (antipsychotic)
metoclopramide
What is the mechanism of action of anticholinergic agents (ACh blockers)?
Block ACh receptors in the inner ear labyrinth
Block transmission of nauseating stimuli to VC
Block transmission of nauseating stimuli from the reticular formation to the VC
Example of ACh blocker?
Scopolamine
What is Scopolamine used for?
Motion sickness
-Patch behind ear
What is the mechanism of action of antihistamine agents (H1 receptor antagonists)?
Block H1 receptors
Prevent cholinergic stimulation in vestibular and reticular areas
Example of antihistamine antiemetic?
Dimenhydrinate (Gravol)
= diphenhydramine + 8-Chlorotheophylline
Diphenhydramine
Cyclizine
What adverse effects are associated with Odansetron?
Dysrhythmia (long Q-T)
What adverse effects are associated with DA antagonists?
Movement disorders
What adverse effects are associated with Scopolamine?
Typical anticholinergic effects
What adverse effects are associated with antihistamines?
Sedation
Typical anticholinergic effects
What is the mechanism of action of glucocorticoids as antiemetics?
Unknown mechanism of action as antiemetic
Examples of antiemetics glucocorticoids?
methylprednisolone
dexamethasone
What are antiemetic glucocorticoid commonly used fro?
Suppress cancer chemotherapy N&V
Example of substance P/neurokinin1 receptor antagonist?
Aprepitant
What is the mechanism of action of substance P/neurokinin1 receptor antagonist: Aprepitant?
Blocks neurokinin1-type receptors in CTZ
-Prolonged duration of action
What is aprepitant used for?
Postoperative and CI N and V
What are Tetrahydrocanabinoids? (THC)
Synthetic derivatives of psychoactive substance in marijuana
What antiemetics were withdrawn in Canada?
Nabilone
Dronabinol
What were Nabilone and dronabinol used for?
N&V associated with chemotherapy
-second-line drug
How should antiemetic drugs be taken?
Prophylactically when appropriate
Chemo= 30 min to 3 hours prior to chemo
Motion sickness:
dimenhydrinate = 1h before travel
Scopolamine patch applied 4h before travel
