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Cause and treatment of nausea and vomiting. Zofran, Phenergan, Reglan mechanism of action.

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#Cinnarizine#cyclizine#promethazine#Scopolamine# Granisetron#ondansetron#dolasetron#tropisetron#chlorpromazine#perphenazine#prochlorperazine#trifluoperazine#Metoclopramide#Domperidone#CTZ#nausea#vomiting#motionsickness#vestibulardisorders#Menière’sdisease#morningsicknessofpregnancy#antiemetic The Vomiting center has receptors for
Nurokinin 1 NK-1,
Cannabinoids CB-1,
serotonin 5-HT3,
dopamine D2,
muscarinic M1
and histamine H1 receptors.
The vomiting center can be activated by afferent fibers
arising from the gastrointestinal track,
Chemoreceptor trigger zone CTZ,
Cerebral cortex and vestibular apparatus.
The CTZ or Chemo receptor trigger zone, is located at the end of fourth ventricle.
CTZ have receptor of serotonin 5-HT3, dopamine D2, muscarinic M1 receptors.
It lies outside of blood brain barrier and stimulate vomiting center in response to
blood borne substances including cytotoxic cancer chemotherapy drugs.
The excessive vestibular stimulation in motion sickness activates the vomiting center
via cholinergic and histaminergic nerve fibers that projected through vestibulocerebellar region of cerebellum.
The irritation of gastric mucosa by chemotheraperautic agents, endogenous toxin and poison leads to
secretion of 5-HT which activate 5-HT3 receptor and this stimuli travel from the gastrointestinal tract
via the nucleus tractus solitarius (NTS) to stimulate vomiting center in the medulla.
Emesis by psychological stimuli such as fear, dread, or obnoxious sights and odors is mediated in
cerebral cortex,
this concept is poorly understood yet.
Nurokinin 1 NK-1, Cannabinoids CB-1 and Histamine could be responsible this effect.
Now we will see the site of action of various antiemetic drugs
Antihistaminic
Antihistaminic antiemetic includes
Cinnarizine, cyclizine and promethazine
Antihistaminic drugs blocks muscarinic M1 receptors or histamine H1 receptors or both types of receptors
in the vestibular tracts that project to the vomiting center and in the CTZ.
Antihistaminic drug Cyclizine is used in motion sickness.
cinnarizine is used in motion sickness and vestibular disorders such as Menière’s disease)
promethazine is used in severe morning sickness of pregnancy.

Antimuscarinics
Antimuscarinics drug Scopolamine is used in motion sickness.
It causes blocking of muscarinic M1 in vestibular tracts.

5-HT3 receptors antagonist
5-HT3 receptors antagonist includes Granisetron, ondansetron, dolasetron, tropisetron and palonsetron.
They are particular value in preventing and treating the vomiting and nausea.
commonly encountered postoperatively as well as that caused by radiation therapy or administration of cytotoxic drugs such as cisplatin.
They prevent emesis by competitively blocking 5-HT3

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