Emetics and Antiemetics: A Review

 

Ashok Rathod*, Amol Rathod, Kundan Tiwari

Student of Pharmacy, SMBT Institute of Diploma Phrmacy Nandi-Hills Dhamangaon, Nashik.

 

ABSTRACT:

Emetics is a complex reflex coordinated by the vomiting centre in the medulla. The afferent and efferent pathaways which cause vomiting are carried by vagus and sympathetic nerves. Chemo-receptor trigger zone is major sensory relay station, present in the lateral border of the area postrema of medulla oblongata. Afferent stimulation like tactile pharyngeal impulses, abryrinthine disturbances, pain, distyension of viscera, psychology factors, increased intracranial pressure, emetic drugs, radiation therapy, electrolyte disturbances, endocrine disturbances, pregnancy etc, cause ‘emesis’ i.e. Vomiting.

 

 

 

INTRODUCTION:

Emetics is a complex reflex coordinated by the vomiting center in the medulla. The afferent and efferent pathways which cause vomiting are carried by vagus and sympathetic nerves. Cheno-receptor Trigger Zone, is major sensory relay station, present in the lateral border of the areas postrema of medulla oblongata.

 

Afferent stimulation like tactile pharyngeal impulses, labyrinthine disturbances, pain, distention of viscera, psychology factors, increased intracranial pressure, emetic drugs, radiation therapy, electrolyte disturbances, endocrine disturbances, pregnancy etc., cause ‘emesis’ i.e. vomiting.

 

Emetic is also known as vomiting. Emetic or vomiting is defined as the process of evacuation or elimination of gastric content.

 

Emetic or vomiting is very helpful for the elimination of harmful substance from stomach and suodenum. Emetics are the drugs which cause the vomiting. It are must be important to use when poison is known to have been swallowed.¹

 

Vomiting is a physical event, it is a forcefully elimination of gastric content through mouth. In the medulla oblongata, vomitinh center or emetic center are situated, that resion is known as Area postrema. In the area postrma. Chemoreceptor Trigger Zone (CTZ) and Nucleus Tractus Soliterius (NTS) is also present.

 

These are pharmaological agents which are used for induction of vomiting. or These are pharmacological agents which when administer the drug they produces vomiting.

 

Emetics, antiemetics, and antidiarrheals are three categories of drugs that affect the gastrointestinal system. Each category of agents has its own distinct use for the relief of patient discomfort. You must be familiar with these agents in order to provide the patient with information which will enhance the medication’s therapeutic effect and/or provide greater patient safety and comfort.¹

 

Vomiting is a common symptom of diverse aetiology and adversely affects the wellbeing of many children. Though in most instances vomiting could resolve spontaneously or with the treatment of etiology, symptomatic treatment of vomiting in children is important. It reduces anxiety in the child and parents, allows successful administration of drugs, oral rehydration salts and other fluids. Hence, antiemetic is considered an effective adjuvant treatment in acute gastroenteritis²_.

 

A number of pharmacologic agents belong to the drug class referred to as antiemetic agents. This review focuses on a group of the phenothiazine, anticholinergic and antihistamine agents with a primary indication for treatment or prevention of nausea and vomiting including: meclizine, metoclopramide, nabilone, prochlorperazine, promethazine, scopolamine and trimethobenzamide. The agents are available in oral, injectable and transdermal formulations.³

 

A number of pharmacologic agents belong to the drug class referred to as antiemetic agents. Antiemetic agents work within a neuronal region to counteract the complex act of vomiting through interactions with cranial nerves and neural networks. Drug classes which have been labeled for use as an antiemetic in the United States include serotonin 5-HT3 antagonists, neurokinin receptor antagonists, phenothiazines, butyrophenones, benzamides, corticosteroids, benzodiazepines, antihistamines, anticholinergic agents, muscarinic receptor antagonists and cannabinoids. This review focuses on the phenothiazine, anticholinergic and antihistamine agents with a primary indication for treatment or prevention of nausea and vomiting. In total, seven agents are included in this review: meclizine, metoclopramide, nabilone, prochlorperazine, promethazine, scopolamine, and trimethobenzamide.³

 

Classification:¹

1.     Centally acting emetics:

      Eg. Apomorphine

2.     Peripherally acting emetics:

      Eg. Mustard, Sodium Chioride

3.     Peripherally as well as centrally acting:

      Eg. Ipecacuanha, Crdiac glycoside

 

Types of vomiting and drugs use for them:⁴

1.     Vomiting due to cytotoxic drugs-Ondansetron + Dexamethsone (corticisteroid). Given 4 and is a good combination.

2.     Vomiting after general anaesthesia (to avoid aspiration pneumonia)- Metoclopromide + Ondansetron.

3.     In pregnancy – usually no drug in the first trimester, if necessary then prothiazines like promethazine with caution of low dose. If there is increased vomiting there may be abortion. Tis condition is called Hyperemetic Gravidarum.

4.     Vomiting due to vertigo – Cyclizine or Prochlorperazine (antihistaminic drugs).

5.     Motion sickness – hyoscine gruop of promethazine, cyclizine medicine is taken before the journey.

 

Antiemetics:¹

Antiemetics are pharmacological agents use specifically to prevent or relieve nausea and vomiting. Or Antiemetics are pharmacological agents which when administer the drug treatment or recover vomiting. Or Vomiting is the forceful expulsion of the cntents of the stomach through the mouth and sometime the nose. The feeling that oneis about to vomit is called nausea, which usually precedes, but does not always lead to, vomiting.

 

The are Five Sources of The Afferent Input To The Vomiting Center:

1.     The chemoreceptor trigger zone has numerous dopamine D receptors, serotonin-HT receptors, opioid receptors, acetylcholine receptors.

2.     Cranial nerve 10 which is activated when the pharynx is irritated, leading to a gag reflex.

3.     The vestibular system which sends information to the drain via cranial 8 (vestibulocochlear nerve). It plays a mojor role in motion sickness and is rich in muscarinic receptors and histamine H’ receptors.

4.     Vagal and emetic nervous system inputs that transmit information regarding the state of the gastointestinal system. Irritation of the GI mucosa by chemotherapy, radiation, distention, or acute infectious gastroenteritis activates the –HT receptor of there inputs.

5.     The CNS mediated vomiting arising from psychiatric disorder and stress from higher brain center.

 

Classification:¹

1.     Anticholinergics

      Eg. Sopalamine, Hyoscine, Dicyclomine.

2.     Antihistaminics

      Eg. Diphenhydramine, Cyclizine, Doxylamine.

3.     Antidopaminergics

      Eg. Clorpromazine

4.     Adjuvant Antiemetics

      Eg. Dexamethasone, Benzodiazepine.

5.     Miscellaneous

      Eg. Haloperidol, Trimethobenzamide, Benzquinamide.

 

Mechanism of Action:¹

Antiemetics produce antiemesis action by acting on either of the receptor sites as follows:

1.     Directly on vomiting centre.

2.     Acting peripherally.

3.     By acting on CTZ (chemo receptor trigger zone)

 

Figure No.01: Pathophysiology of Emesis⁵

 

Figure No. 02: Physiology of Nausea and Vomiting

 

Critical Facts⁴:

1.     Emetics can act either centrally (on the CTZ or the vomiting center) or peripherally on the GI tract or both. Therefore, in determining the mechanism of action of emetic and antiemetic drugs, it is important to consider both the location of the receptors in a particular pathway, and whether the receptors are inside or outside the blood-brain barrier.

2.     Use of IPECAC to induce vomiting is no longer recommended. Problems can arise if it is administered with activated charcoal or if the suspected poison is corrosive, a petroleum distillate or a rapidly-acting convulsant.

3.     5HT3 antagonists (DOLASETRON, GRANISETRON, ONDANSETRON) are the only agents that are truly effective in ameliorating cancer chemotherapy induced emesis (esp. caused by cisplatin). SCOPOLAMINE is the most effective agent for the treatment of motion sickness.

4.     The newest antiemetic drug is APREPITANT, a neurokinin receptor antagonist, which may be of use in preventing the delayed phase of cancer chemotherapy induced emesis.⁶

 

Causes:⁷

Causes in the digestive tract:

·         Gastritis (inflamation of the gastric wall, usually by viruses).

·         Gastroenteritis.

·         Bowel obstruction.

 

Overe acting:

·         Food allergies.

·         Food poisaning.

·         Pregnancy

 

 

Causes in the sensory system:

Movement: motion sickness

 

Causes in the brain:

·       Central haemorrhage.

·       Migration.

·       Brain tumors.

 

Metabolic disturbances (these may irritate the stomach and that coordinate vomiting).

·         Hypercalcemia, Hypoglycemia, Hyperglycemia.

·         Adrenal insufficiency.

 

Figure No.03: Effect of Drug (Metoclopramide)

 

Preparation:¹

●	Scopolamine hydrobromide	-	0.6 mg to 1 mg Subcutaneously.
●	Prochlorpromazine	-	2 mg to 5 mg
●	Clorpromazine	-	10 mg to 15 mg

 

Therapeutic Application / Uses:⁸

·       As an antiemetic especially in post – operative vomiting.

·       To treat cotrol vomiting during cancer therapy.

·       To treat reflex esophagitis.

·       To treat vomiting due to motion sickness.

·       To treat vomiting during pregnancy. (along with pyridoxin)

·       To treat vomiting during GIT. Disturbances.

·       To treat vomiting due to psychological reasons.

 

REFERENCES:

1.        S.R. Kale and R.R. Kale “Pharmacology And Toxicology”, Nirali Prakashan, Sixteenth Edition Jun 2014, P. 11.10-11.12.

2.        S Sri Ranganathan, K Mayurathan, R Fernandopulle, A survey on antiemetics prescribed for children in some selected districts of Sri Lanka, Sri Lanka Journal of Child Health, 2010; 39: P. 93-97.

3.        Melissa Archer, Antiemetics Drug Class Review, Final Report March 2014, P. 5-6.

4.        Dr. Janet Fitzakerley, Decontamination Agents and Antiemetics, Gastrointestinal Hepatobiliary System, 2007 P. 1-8.

5.        Dr. Imad A-J Thanoon “Antiemetic Drugs” Slideshow.Com.

6.        FSK Barar, Essential of Pharmacotherapeutics, S. Chand, Fifth edition 2009, P. 531-532.

7.        KD Triparthi, Essential of Medical Pharmacology, Jaypee brothers medical publishers, Sixth edition 2009, P. 639-640.

8.        Rang & Dale’s, Pharmacology, Churchill Livingstone Elsevier, Sixth edition 2007, P. 390-393.

 

 

 

 

Received on 18.07.2018         Modified on 07.09.2018

Accepted on 27.09.2018       ©A&V Publications All right reserved