Vomiting Agents - An Overview

Introduction:

Several reflex mechanisms can be seen in the human body, which is helpful in maintaining the normal functioning of the body. Usually, vomiting is a harmless phenomenon. But, excessive vomiting may cause serious illness. Certain chemical substances may cause excessive vomiting.

What Is the Mechanism of Vomiting?

Nausea and vomiting are considered protective mechanisms that help the body from ingestion of unpleasant substances. Through vomiting, a person throws out a toxic or unpleasant substance. The unpleasant sensation before vomiting is known as nausea. In general, both of these sensations can be felt just one after another. Just as with every physiological process, the process of nausea and vomiting is also controlled by several neuro-physiological and chemical pathways.

The two main centers that are associated with vomiting are the vomiting center in the brain and the chemoreceptor trigger zone (CTZ). The vomiting center is located in the fourth ventricle of the brain. This is known as postrema. This area is located bilaterally and lacks the blood-brain barrier. But this area is strongly influenced by circulating external stimuli in the blood and cerebrospinal fluid. The nucleus of the solitary tract present in this location receives neural stimuli from the area postrema and the sensory vagal afferents. This area also receives signals from the splanchnic nerves (nerve supply autonomic sensation to the abdomen and pelvis), vestibular apparatus of the inner ear, cerebellum, and cerebral cortex. The medial subnucleus located within the nucleus of the solitary tract acts as the main site for the central nervous system modulation and vomiting reflexes. Nerve stimuli for vomiting from the nucleus of the solitary tract go to the gastrointestinal tract via the dorsal motor nucleus of the vagus. The dorsal motor nucleus of the vagus regulates the motility of the gastrointestinal tract and regulates the vomiting reflex.

The five receptors that are associated with vomiting are muscarinic (M1), dopaminergic (D2), histaminergic (H1), 5-hydroxytryptamine or 5-HT3 (serotonin), and neurokinin NK1 (substance P) receptor. The chemoreceptor trigger zone in the brain is rich in dopamine (D2) and 5-HT3 (serotonin) receptors. This chemoreceptor trigger zone is located in the fourth ventricle of the brain within the medulla oblongata. The receptors in this region are triggered by cytotoxic agents like chemotherapeutic agents. The vestibular nucleus in the brain consists of receptors like histaminergic (H1) and muscarinic (M1). These two receptors are also present in the vomiting center. Motion sickness and morning sickness is responsible for the activation of these receptors. In the gastrointestinal tract, receptors present are neurokinin NK1 (substance P) and 5-hydroxytryptamine or 5-HT3 (serotonin).

What Are the Factors Associated With Vomiting?

The factors that are associated with vomiting are:

1. Pathological Conditions: Different pathological conditions, specifically gastrointestinal tract infections, and systemic infections, are one of the main causes of vomiting. Other than this, conditions like diabetes mellitus, diabetic ketoacidosis (a diabetic condition that leads to accumulation of ketone in the body), hypercalcemia (excessive calcium present in the blood), hyperparathyroidism, hyperthyroidism, and uremia (increased level of urea in the blood). Disorders of the nervous system like epilepsy, cerebral edema (accumulation of fluid in the brain), meningitis (inflammation of the protective membrane of the spinal cord and the brain), and otitis media (infection in the ear) are associated with vomiting. Obstructive conditions in the gastrointestinal tract, like tumors, small intestine obstruction, and volvulus (twisting of the intestine), are responsible for vomiting.

2. Drugs: Several drugs like chemotherapeutic agents, non-steroidal anti-inflammatory drugs (like Ibuprofen and Aspirin), antibiotics (like Metronidazole and Ceftriaxone), contraceptives, and immunosuppressive drugs are associated with vomiting.

3. Psychological Conditions: Psychological conditions like anger, stress, depression, sudden emotional changes, and trauma may cause vomiting.

4. Environmental Factors: Environmental factors like bad smells and any unpleasant events are also responsible for vomiting.

5. Toxic Agents: Toxic agents are one of the most important factors associated with vomiting. Arsenic and certain chemical warfare agents are associated with vomiting.

6. Others: Surgical interventions, seasickness, motion sickness, and mountain sickness are the causative factors for vomiting.

What Are the Vomiting Agents?

Vomiting agents are the substance that is responsible for vomiting. Such agents are:

1. Arsenic: Arsenic is one of the most commonly found chemical substances on the earth's surface. Arsenic poisoning is one of the main causes of vomiting. One of the main sources of arsenic in the body is the consumption of water from the soil. Organic arsenic compounds also play a vital role in arsenic toxicity. Organic arsenic compounds are methyl and phenyl derivatives of arsenic acid that are used in agriculture. In the gastrointestinal tract, monomethyl arsenic acid (MMA), one of the key arsenic compounds, causes diarrhea and vomiting. Roxarsone, another organic arsenic compound extensively used in the poultry industry, is responsible for arsenic toxicity. Vomiting and gastrointestinal hemorrhage are caused by this substance.

2. Irritant Incapacitants: These are toxic substances mainly used as riot control agents. These are organic arsenic compounds, also known as adamsite. These compounds were first manufactured in 1915 in Germany and were used extensively in the first world war. These compounds are diphenylamine arsine (DM), diphenylchloroarsine (DA), and diphenylcyanoarsine (DC). Other compounds belonging to this group are ethyldichloroarsine, methyldichloroarsine, and phenyldichloroarsine. The effect starts within one to two minutes after exposure and lasts for more than 2 hours.

3. Ipecacuanha: This is a plant derivative mainly used in homeopathic practice. It is derived from a plant named Carapichea ipecacuanha. This is used as an emic substance to remove toxic substances from the body. This can also be used as an anti-amebic drug. This drug causes gastric irritation and increases gastric motility, and causes vomiting.

Conclusion:

Vomiting is a reflex mechanism to remove the contents of the gastrointestinal tract. In general, it is a type of protective mechanism. But in some cases, it is induced by several pathological conditions. Some toxic substances may cause vomiting. These substances are mainly derived from arsenic. Such compounds are known as vomiting agents. Certain drugs may also be used as vomiting agents. Vomiting caused by chemical substances may cause serious complications.