• Dopamine Antagonists
• Serotonin Antagonists (5HT3 Receptor Antagonists)
• Neurokinin Antagonists
• Antihistamines
• Corticosteroids
• Benzodiazepines
• Cannabinoids

1. What Are Dopamine Antagonists?

Dopamine antagonists are drugs that block the D₂ dopamine receptor in the brain and gastrointestinal neurons by preventing dopamine binding and activation of the receptor D₂ to induce the excitation of neurons.

Dopamine is an organic chemical involved in the transmission of instructions between neurons to control movement and reward-motivated behavior [2].

Dopamine performs its action by binding to dopamine-specific receptors found on the cell surface of neurons in the nervous system.

There are 6 types of dopamine receptors known as D₁, D₂, D_3, D₄, and D₅.

The activation of D₁ and D₅ through dopamine biding can induce the excitation or inhibition of the function of target neurons, while the activation of D₂, D_3, and D₄ by dopamine results in the inhibition of target neurons.

Dopamine antagonists include the following antiemetic drugs:

• Metoclopramide (Antiemetic class: Benzamides) also known as Primperan and Reglan
• Domperidone (Antiemetic class: Benzimidazoles) also known as Motilium
• Prochlorperazine (Antiemetic class: Phenothiazines) also known as Compazine and Stemetil
• Chlorpromazine (Antiemetic class: Phenothiazines) also known as Thorazine and Largactil
• Droperidol (Antiemetic class: Butyrophenones) also known as Inapsine, Droleptan, and Dridol
• Haloperidol (Antiemetic class: Butyrophenones) also known as Haldol and Serenace
• Olanzapine (Antiemetic class: Atypical Antipsychotics) also known as Zyprexa

In addition to blocking the dopamine receptor D₂, Prochlorperazine, Droperidol, Haloperidol, and Olanzapine also block serotonin, histamine, adrenergic, and muscarinic receptors [1].

2. What Are Serotonin Antagonists (5HT3 Receptor Antagonists)?

Serotonin antagonists or 5HT3 Receptor Antagonists are drugs that block 5HT3 receptors in the brain and gastrointestinal neurons by preventing serotonin binding and activation of the 5HT3 receptor to induce the excitation of neurons [3].

Serotonin is a chemical messenger involved in the neurotransmission of information related to mood, reward, learning, memory, and cognition.

Serotonin antagonists include the following antiemetic drugs:

• Ondansetron (Zofran)
• Granisetron (Kytril, Sancuso)
• Palonosetron (Aloxi)
• Tropisetron (Navoban)
• Dolasetron (Anzemet)

3. What Are Neurokinin Antagonists?

Neurokinin antagonists are drugs that block neurokinin receptor type 1 (NK₁) on neurons of the brain and peripheral nervous system by preventing substance P binding and activation of neurokinin receptor type 1 (NK₁) to induce the excitation of neurons [4].

Neurokinin receptor type 1 (NK₁) expression on cells is not limited to neurons but is also found on other non-neuronal cell types.

Substance P is a neuropeptide that functions as a neurotransmitter or neuromodulator and is involved in inflammation, vasodilatation (dilatation of vessels), pain, vomiting, mood, anxiety, and learning.

Neurokinin antagonists include the following antiemetic drugs:

• Aprepitant (Emend for oral use)
• Fosaprepitant (Emend used IV)
• Netupitant
• Netupitant/Palonosetron combination (Akynzeo)

4. What Are Antihistamines?

Antihistamines are drugs that block the H1 receptor on neurons of the brain and peripheral nervous system by preventing histamine binding and activation of the H1 receptor to induce the excitation of neurons.

The H1 receptor is also expressed on the surface of vascular endothelial cells, smooth muscles, and the heart.

Histamine is a well know actor in local immune responses, and is produced by mast cells and basophils; however, it is also an important neurotransmitter involved in itching following inflammation, and in the regulation of sleep-wakefulness cycle [5].

Antihistamines include the following antiemetic drugs:

• Doxylamine (Unisom)
• Cyclizine (Marezine, Valoid, Nausicalm)
• Pheniramine (Avil)
• Promethazine (Phenergan)

Doxylamine, Cyclizine, and Pheniramine also block muscarinic receptors, while Promethazine blocks dopamine D₂ receptors [1].

5. What Are Anticholinergics?

Anticholinergics block muscarinic receptors on neurons of the vestibular nuclei, and the vomiting and chemoreceptor center in the medulla of the brain by preventing acetylcholine binding and activation of the muscarinic receptors to induce the excitation of neurons.

Acetylcholine is an organic chemical involved in the transmission of instructions between neurons and muscles known as neuromotor or neuromuscular transmission, and between neurons that transmit information for brain organs and glands that are involved in attention, wakefulness, learning, memory (short-term memory), motivation, mood and emotion [6].

Hyoscine is an antihistamine used as an antiemetic and is also known as Transdemscop and Kwells.

6. What Are Benzodiazepines?

Benzodiazepines prevent the excitation of neurons by enhancing the effect of GABA on GABA_A receptors.

GABA (Gamma-Aminobutyric acid) is a chemical messenger and the major inhibitor of neurotransmission by reducing nerve impulses (action potential) [7].

Lorazepam is a benzodiazepine used as an antiemetic and is also known as Ativan.

7. What Are Corticosteroids?

Corticosteroids are anti-inflammatory drugs that inhibit the synthesis and release of the proinflammatory mediators, prostaglandins, by the brain.

Prostaglandins are produced and released by almost all types of cells and act on the uterus, platelets, vessels, and mast cells [8].

Dexamethasone is the anti-inflammatory drug used as an antiemetic and known by the trade names, Dextenza, Ozurdex, Cortidex, and Neofordex.

8. What Are Cannabinoids?

Cannabinoids are substances found in cannabis that activate the CB1 cannabinoid receptors in the brain and peripheral nervous system resulting in the modulation of the release of neurotransmitters [9].

Cannabinoids include the following antiemetic drugs:

• Tetrahydrocannabinol (Marinol, Syndros)
• Nabilone (Cesamet, Canemes)
• Nabiximols (Sativex)

9. When do you need an antiemetic drug?

Antiemetics are used for the treatment of nausea and vomiting associated with the following conditions:

• Gastroenteritis
• Chemotherapy-Induced Nausea and Vomiting
• Migraine-Related Nausea and Vomiting
• Vertigo
• Opioid-Induced Nausea and Vomiting
• Radiation-Induced Nausea and Vomiting
• Post-Surgery Nausea and Vomiting

9.1. Gastroenteritis

Gastroenteritis is an inflammation of the gastrointestinal tract due to viral, bacterial, or parasitic infections. It manifests with symptoms including abdominal pain, nausea, and vomiting.

Nausea and vomiting resulting from gastroenteritis can be treated using serotonin antagonists such as ondansetron and dopamine antagonists such as metoclopramide or prochlorperazine [10].

9.2. Chemotherapy-Induced Nausea and Vomiting

Chemotherapy compounds such as Paclitaxel can induce nausea and vomiting which can be blocked using the 5HT3 receptor antagonists (serotonin antagonists).

Induced nausea and vomiting by cisplatin chemotherapy require a combination of neurokinin antagonists, serotonin antagonists, and dexamethasone [11].

Some studies suggested the use of cannabinoids to reduce Chemotherapy-Induced Nausea and Vomiting [12].

9.3. Migraine-Related Nausea and Vomiting

A migraine is a severe form of headache that manifests as an excruciating pain on one side of the head accompanied by a feeling of sickness and an increased sensitivity to light and sound.

Migraine-related nausea and vomiting are treated using Metoclopramide (Primperan, Reglan) [13]. Dopamine antagonists such as prochlorperazine or chlorpromazine have also shown efficacity [14].

9.4. Vertigo

The treatment of vertigo– and motion sickness-induced nausea and vomiting, involves the use of antihistamines such as promethazine, dopamine antagonists such as prochlorperazine, and anticholinergics such as hyoscine [15].

9.5. Opioid-Induced Nausea and Vomiting

Treatment of opioid-induced nausea and vomiting is not well-defined; however, some studies showed the efficacy of some antiemetics such as the serotonin antagonist, Ondansetron (Zofran) [16].

9.6. Radiation-Induced Nausea and Vomiting

Radiation-Induced Nausea and Vomiting such as after radiotherapy, are treated with a serotonin antagonist and dexamethasone [17].

9.7. Post-Surgery Nausea and Vomiting

The treatment of post-surgery nausea and vomiting was suggested to use the serotonin antagonists, dexamethasone, the dopamine antagonist, droperidol, and the antihistamine, cyclizine [1].

Conclusion

Antiemetics are drugs used to treat nausea and vomiting associated with gastroenteritis, vertigo, migraine, surgery, opioids, radiation, and chemotherapy. Some of the antiemetics are more efficient for the treatment of a specific condition, while others have a larger effect range.

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• Redness
• Swelling
• Heat
• Pain
• Loss of Function

1. What Is the Main Cause of Inflammation in the Body?

There are many causes of inflammation that is triggered by the body’s immune system:

• Injury such as a splinter, scrapes, trauma, or any damage caused by a foreign object.
• Pathogens, including viruses, bacteria, parasites, or fungi
• Chemicals such as glucose, fatty acids, chemical irritants (e.g., acids), toxins, and alcohol
• Radiation such as sunburns
• Biological such as damaged cells in the body

2. What Happens During Inflammation?

Inflammation involves the contribution of different immune cells which release substances known as inflammatory mediators, including hormones such as histamine and bradykinin [1].

These inflammatory mediators induce vasodilation (dilatation of the vessels) which promotes the blood flow in the injured tissue and the recruitment of inflammatory cells (neutrophils, monocytes, and endothelial cells) to the site of injury.

The vasodilatation and the blood rush into the injured tissue result in redness and heat which are 2 signs of acute inflammation.

The pain associated with inflammation is caused by the irritation of local nerves by the inflammatory mediators.

These inflammatory cells have specific roles during acute inflammation:

• Neutrophils initiate the phagocytosis and killing of pathogens to decontaminate the wound, while also promoting cell proliferation and angiogenesis.
• Monocytes also contribute to the phagocytosis and killing of pathogens, and become macrophages, which remove dead cells, and support cell proliferation and tissue restoration following injury.
• Endothelial cells are the building blocks for vessels, and during wound healing, these cells generate new vessels (angiogenesis) to satisfy the metabolic demands of the highly proliferative healing tissue. 

Depending on the site of injury, a transitory loss of function can be observed due to tissue damage, swelling, or pain during inflammation.

3. How long Does Inflammation Last For?

Inflammation can be acute lasting for a few days (2-3 days) or chronic which lasts for a longer time until the insult is resolved.

What Are the Outcomes of Inflammation?

The resolution of acute inflammation (initial inflammation) depends on the causes and the extent of tissue damage. It is characterized by the following outcomes:

• Complete repair of the injured tissue and without scars
• Resolution of the inflammation with the formation of a scar or fibrosis
• Formation of an abscess
• Chronic inflammation if the initial inflammation persists and remains unresolved

The complete repair of the injured tissue or the formation of scars is mediated by a process known as wound healing.

Wound healing is a natural reaction of our body to tissue damage and involves crosstalk between different cells, cytokines, inflammatory mediators, and the vascular system to repair the damaged tissue.

4. What Are the Most Common Inflammatory Diseases?

The most common inflammatory diseases are associated with chronic mediated inflammation which includes the following diseases [2]:

• Rheumatoid Arthritis
• Cardiovascular diseases
• Inflammatory Bowel Disease (IBD) 
• Allergic Asthma
• Chronic obstructive pulmonary disease (COPD)
• Diabetes
• Chronic Kidney Disease
• Cancer

4.1. Rheumatoid Arthritis

Rheumatoid arthritis is due to a local chronic inflammation that results in the infiltration of immune cells into the joints and the release of inflammatory mediators such as cytokines.

4.2. Cardiovascular diseases

Atherosclerosis is associated with a chronic inflammation that leads to heart diseases such as stroke, and myocardial infarction.

4.3. Inflammatory Bowel Disease (IBD)

Inflammatory Bowel Disease (IBD) is a group of chronic inflammatory disorders affecting the bowels that are caused by ulcerative colitis (inflammation of the colon due to ulcer) or Crohn’s disease.

4.4. Allergic Asthma

Allergic asthma is due to the inflammation of the airways caused by the inhalation of an allergen which results in their swelling and tightening affecting breathing.

4.5. Chronic obstructive pulmonary disease (COPD)

COPD is a chronic inflammatory lung disease due to the exposure of the airways to harmful particles or gases causing inflammation that obstruct airflow in the lung leading to breathing difficulties.

4.6. Diabetes

One of the characteristics of diabetes is the infiltration of immune cells, such as macrophages, into pancreatic tissue, and their release of pro-inflammatory molecules responsible for inflammation.

4.7. Chronic Kidney Disease (CDK)

Chronic kidney disease or chronic kidney failure is a progressive loss of the function of the kidney resulting from the accumulation of body wastes and fluids in the blood.

One of the causes of chronic kidney disease is the inflammation of the glomeruli that filter blood for the elimination of waste and fluids in urine.

4.8. Cancer

Chronic inflammation is one of the characteristics of different types of cancer from various origins (Prostate, hepatic, colorectal, ovarian, pancreatic, and lung cancers).

4.9. Neurodegenerative diseases

Neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease are associated with the production of proinflammatory molecules by the brain resident immune cells and microglia which cause brain damage.

5. What Is the Difference Between Inflammation and Infection?

Infections cause inflammation which is a natural process by which the body’s immune system fights against pathogens, including bacteria, viruses, fungi, or parasites.

6. How Do You Get Rid of Inflammation in the Body?

Unlike acute inflammation, chronic inflammation can last for a longer period, and therefore, requires management and treatment through lifestyle changes or medications [3].

6.1. Lifestyle changes

6.1.1. Diet

A diet rich in glucose and processed food rich in saturated fat and trans fats promotes inflammation leading to cardiovascular diseases and type 2 diabetes. Hence, a low glucose diet and avoiding processed food can prevent inflammation.

A diet rich in vegetables and fish oils, nuts, mung bean, green and black teas, and certain species (e.g., ginger, turmeric) can prevent or reduce inflammation as they contain antioxidants and polyphenols which have anti-inflammatory properties.

6.1.2. Physical Activity

In addition to weight loss associated with exercising, physical activity also results in energy consumption with reduces the levels of proinflammatory molecules in the body.

6.2. Medications

The most used anti-inflammatory medications include nonsteroidal anti-inflammatory drugs (NSAIDs) and corticosteroids. 

Nonsteroidal anti-inflammatory drugs (NSAIDs) such as naproxen, ibuprofen, and aspirin, alleviate pain by inhibiting the function of the enzyme cyclooxygenase (Cox) involved in the synthesis of the proinflammatory molecules, prostaglandins.

Corticosteroids are prescribed for some inflammatory conditions such as arthritis, asthma, systemic lupus, and sarcoidosis.

Conclusion

Acute inflammation is a natural process by which the body’s immune system responds to injuries and infections. Acute inflammation takes a few days to resolve, leading to a complete repair of damaged tissues, fibrosis (scars), formation of an abscess, or chronic inflammation.

Chronic inflammation can be associated with several inflammatory diseases such as rheumatoid arthritis, allergic asthma, cancer, diabetes, cardiovascular diseases, chronic kidney disease, COPD, inflammatory bowel disease, and neurodegenerative diseases.

The treatment of chronic inflammation includes lifestyle changes, physical activity, and medications using anti-inflammatory drugs such as NSAIDs and corticosteroids.

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