Vomiting - Phamacology of Emetics and Antiemetics

A lot of us vomit and we think it is a bad thing, anyways for me it isn't something bad that needs to be surpressed but in cases where it is a symptom of an altered function in the body, then it could be suppressed or induced and that is the function of Emetics. To continue, let's first understand the pathophysiology of vomiting.

Vomiting center is in the medulla with M1 and H1 receptors. This receptors can be stimulated by different pathways such as the cerebral cortex which is responsible for sending signals of sight and smell, and that is why when you see, smell, or think of something bad, you immediately want to vomit causing nausea known as Anticipatory Emesis. Another way is through the vestibular nuclei which could be triggered by motion in the form of motion sickness. Vomiting can be caused by the GIT and pharynx as they possess enterochromaffin cells which releases serotonin when there is an irritation to the gastrointestinal tract which will cause the vomiting center to be triggered. Vomiting can also be stimulated by visceral pain where prednisone and substance P associated with pain in the area stimulates the neurokinin receptors in the spinal cord which causes vomiting.

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The Chemoreceptor Trigger Zone is located at the dorsal surface of the medulla oblongata, and it recieves imput from hormones and drugs that are bloodborne. It is made up of cannabinoid, opioid, serotinin, dopamine (D2) receptors, and substance P which can be stimulated by hormones and drugs since it has no blood brain barrier thereby stimulating the vomiting center.

Anti-emetics antagonist are 5HT3 antagonist, D2 antagonist, M1 antagonist, H1 antagonist and NK1 antagonist while this are antagonist, agonist that can be used to stop vomiting are cannabinoid agonist. The antagonizing of the receptors responsible for vomiting would prevent vomiting fully. Using emetics is a way to stimulate vomiting by stimulating the Chemo Trigger Zone (CTZ) or the irritation of the gastrointestinal tract by irritating the gastric mucosa. This can be done in cases of poison or indigestion so the person can vomit and this ematic include Ipecap syrup, Subcutaneous Apomorphine, and common salt. While this is useful for vomiting, it should not be given to unconcious patient.

Anti-ematics can be classified in to the 5HT3-r antagonists, Anti histamine (H1 antagonist), Anticholinergics, D2 antagonist, and NK1 Receptor antagonist, prokinetic agents, Cannabinoids and Adjuvants such as glucocorticoid and benzodiazepine.

The 5HT3 receptor antagonists block the vegal afferent from the gut to the vomiting center, and block impulses to the nucleus of tractus solitarius. 5HT3 receptor antagonists drugs are Ondansetron, granisetron, Palonosetron, and Ramosetron. Anti histamine (H1 antagonist) drugs block the H1 receptors on the vestibular nucleus and vomiting center, as thay have central anticolinergic activity. They are used for motion sickness as they have sedative functions. and post operation vomiting. Drugs to be used are Diphenhydromine, promethazine, cyclizine, and meclazine. They can have side effects such as drowsiness, and driness in the mouth.AntiCholinergics are also used for motion sickness as the block the afferents from vestibular nucleus and block the M1 receptors on the vestibular apparatus and the vomiting center. Scopolamine is an example of Anti Cholinergics drugs.

D2 antagonists are anti cholinergic, anti-H1, and it blocks the Chemo Trigger Zone. This drugs are potent but they can cause distonia and trauma. They are used in chemo therapy, radio therapy, and uremia. D2 antagonists drugs are prochlorperazine, Chlopromazine and so on.NK1 receptor antagonist drug block the NK1 receptor, they block substance P action, and the action of Chemo Trigger Zone. The drugs are Aprepitant, and Fosaprepitant. These drugs can cause Diarrhea, and flatulence. Prokinetic agents promote cordinated movement of upper gastrointestinal tract. Prokinetic agents Drugs include Metoclopramide which acts in central as a D2 antagonist and peripheral where it antagonizes 5HT3. Cannabinoids is the last resort when patients do not respond to other anti-emetics. They act on CB1 receptors in the Chemo trigger zone and the drugs are nabilone and Dronabinol but they can lead to drug dependense, sedation, central and sympathetic issues such as hallucinations, techycardia, and so on.

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https://www.ncbi.nlm.nih.gov/books/NBK532303/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3006663/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8198651/

https://www.ncbi.nlm.nih.gov/books/NBK537133/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3165951/

https://www.ncbi.nlm.nih.gov/books/NBK513318/

https://go.drugbank.com/categories/DBCAT002341

https://www.ncbi.nlm.nih.gov/books/NBK470394/

https://go.drugbank.com/categories/DBCAT000772

https://go.drugbank.com/categories/DBCAT000665

https://www.ncbi.nlm.nih.gov/books/NBK555893/