• 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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• Meclizine (Antivert)
• Dimenhydrinate (Dramamine)
• Diazepam (Valium)
• Lorazepam (Ativan)
• Metoclopramide (Reglan)
• Prochlorperazine (Compazine)
• Promethazine (Phenergan)

1. What Are the Most Common Causes of Vertigo?

Vertigo can be caused by acute unilateral vestibular lesions (Labyrinth or vestibular nerve) known as peripheral vertigo, or by lesions affecting the cerebellum or brainstem, known as central vertigo. The most common causes of vertigo are associated with the following disorders:

• Benign Paroxysmal Positional Vertigo
• Acute Vestibular Neuronitis
• Labyrinthitis
• Ménière’s Disease
• Migraine
• Anxiety disorders
• Vascular Ischemia or Stroke
• Acoustic Neuroma
• Cerebellar Degeneration
• Cerebellar Tumor
• Multiple Sclerosis
• Vestibular Ototoxicity
• Perilymphatic fistula

1.1. What Is Benign paroxysmal positional vertigo (BPPV)?

Benign paroxysmal positional vertigo (BPPV) is a disorder of the inner ear labyrinth that manifests with symptoms of episodic vertigo, loss of balance, dizziness, nausea, and vomiting.

It is caused by the displacement of calcium crystal structures within the inner ear saccule and utricle known as uroliths which help hair cells (stereocilia) in converting sound and head movement into neural signals.

The misplacement of these calcium crystal structures can be due to sudden head movement or head trauma [2].

1.2. What Is Labyrinthitis?

Labyrinthitis is the inflammation of the inner ear labyrinth causing symptoms such as vertigo, hearing loss, nausea, vomiting, and tinnitus [3].

Labyrinthitis is caused by viral and bacterial infection, and rarely by the formation of new bone in the inner ear labyrinth (Labyrinthitis Ossificans).

1.3. What Is Acute Vestibular Neuronitis?

Vestibular neuritis is the inflammation of the vestibulocochlear nerve which transmits to the brain, sound, and head movement neural signals that are received from hair cells.

Vestibular neuritis may be caused by infection with viruses such as herpes simplex virus (HSV-1), measles, mumps, or chickenpox [4].

1.4. What Is Ménière’s Disease?

Ménière’s disease is a disorder of the inner ear characterized by recurrent vertigo, tinnitus, and hearing loss. The causes of these diseases are unknown and may involve genetic and environmental factors [5].

1.5. What Is Vestibular Migraine?

Vestibular migraine is vertigo with migraine that does not necessarily manifest with headaches. The causes of vestibular migraine are unknown; however, genetic factors may be involved [6].

Vestibular migraine has been associated with Meniere’s disease and Benign paroxysmal positional vertigo (BPPV).

1.6. What Are Anxiety disorders?

Anxiety disorders are the most prevalent psychiatric disorders characterized by uncontrollable worries and fear associated with emotions, thoughts, ideas, and places.

Anxiety disorders can significantly affect the daily life of an individual and commonly manifest with symptoms, including irritability, focusing difficulties, chest pain, increased heart rate, and abdominal discomfort [7].

1.7. What Is Vascular Ischemia or Stroke?

Vascular ischemia or stroke are characterized by the reduction (ischemia) or absence (Stroke) of blood supply to the cerebellum or brainstem resulting in their damage and leading to acute vertigo.

1.8. What Is Acoustic Neuroma?

Acoustic neuroma or vestibular schwannoma is a tumor that develops from the Schwann cells on the vestibulocochlear nerve [8].

Schwann cells produce the Schwann myelin sheet that insulates nerves and helps with the transmission of nerve impulses.

The pressure from an acoustic neuroma on the vestibulocochlear nerve results in hearing loss, tinnitus, and unsteadiness.

Acoustic neuroma may be associated with neurofibromatosis type 2, a genetic disease characterized by tumors that grow along nerves.

1.9. What Is Cerebellar Degeneration?

Acquired cerebellum disorders are characterized by cerebellar degeneration associated with ischemic or hemorrhagic stroke, which limits blood flow or oxygen to the cerebellum.

These acquired disorders can also be associated with Multisystem atrophy, cerebellar cortical atrophy, and olivopontocerebellar degeneration.

Transmissible spongiform encephalopathies, such as Creutzfeldt-Jakob disease, can cause inflammation in the brain, including the cerebellum.

Damages to the neurons’ myelin sheath during diseases, such as multiple sclerosis can also affect nerve cells of the cerebellum.

Chronic alcohol abuse can lead to temporary or permanent cerebellar damage that can cause cerebellar degeneration.

Paraneoplastic disorders that are triggered by the body’s own immune system in response to cancers (e.g., lung, ovarian, lymphatic, or breast cancer) can result in the production of substances that cause immune system cells to attack neurons in the cerebellum leading to cerebellar degeneration.

1.10. What Is a Cerebellar Tumor?

Cerebellar tumors are lesions that mainly manifest with severe symptoms due to the compression of the cerebellum and adjacent brainstem or obstruction of cerebrospinal fluid (CSF) flow within the fourth ventricle [9].

The most common cerebellar are low-grade-gliomas which can cause symptoms such as gait ataxia and nystagmus

1.11. What Is Multiple Sclerosis?

The axons of neurons are covered by a sheath of a fatty acid (lipid), known as myelin, which insulates them and increases the rate of nerve impulses.

In multiple sclerosis (MS), the myelin sheath is damaged through a process called demyelination which disrupts the capacity of the affected neurons to conduct nerve impulses.

It is proposed that multiple sclerosis (MS) is due to a mix between genetics and infections; however, there is no evidence yet to support these hypotheses.

1.12. What Is Vestibular Ototoxicity?

Ototoxicity is the poisoning of the ear by chemicals or drugs that leads to damage to the inner ear causing balance and hearing difficulties.

1.13. What Is Perilymphatic fistula?

Perilymphatic Fistula is an abnormal opening between the inner ear and the surrounding structures due to congenital abnormalities or an injury (Head trauma, barotrauma) [10].

The symptoms of Perilymphatic Fistula include hearing loss, vertigo, tinnitus, dizziness, spatial disorientation, and nausea.

2. How Do I Know If I Have Vertigo or Dizziness?

Although dizziness and vertigo have been interchangeably used, dizziness is a perception associated with feeling light-headed and unsteady, while vertigo is the perception of being in movement or that your surrounding is in movement. 

3. How Is Vertigo Treated?

3.1. What Are Vestibular Rehabilitation Exercises?

Vestibular rehabilitation exercises are used in combination with antivertigo drugs and are aimed at training the brain to use different visual and proprioceptive signals to maintain gait and balance [11].

3.2. What Are Antivertigo Drugs?

Antivertigo drugs are used for the treatment of acute vertigo that lasts for hours to days.

3.2.1. What Is Meclizine?

Meclizine (Antivert, Bonine) is an antihistamine drug that blocks H1 receptors which prevents their activation by histamine.

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 the sleep-wakefulness cycle [12].

Meclizine blockage of histamine binding to H1 receptors may reduce the function of the sensory vestibular organs and increase vestibulocochlear blood flow [13].

3.2.2. What Is Dimenhydrinate?

Dimenhydrinate (Dramamine, Draminate) is an antihistamine drug that blocks H1 receptors which prevents their activation by histamine. It has also an anticholinergic activity by inhibiting the activity of the neurotransmitter acetylcholine [14].

3.2.3. What Is Diazepam?

Diazepam (Valium) belongs to the class of drugs known as benzodiazepines which 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).

Therefore, it has an opposite action to that of glutamate and ensures balanced neurotransmission [15].

Benzodiazepines are used for the treatment of anxiety, panic disorder, sleep disorders (e.g., insomnia), epileptic seizures, as a muscle relaxant, and for the treatment of alcohol withdrawal.

3.2.4. What is Lorazepam?

Lorazepam (Ativan) also belongs to the benzodiazepines family of drugs which act by preventing the excitation of neurons through enhancing the effect of GABA on GABA_A receptors.

3.2.5. What Is Metoclopramide?

Metoclopramide (Reglan) is an antiemetic (prevent nausea and vomiting) drug that is mainly used for post-chemotherapy nausea and vomiting.

Metoclopramide is a blocker of serotonin receptors known as 5-HT3 receptors. Serotonin is a chemical messenger involved in the neurotransmission of information related to mood, reward, learning, memory, and cognition. 

3.2.6. What Is Prochlorperazine?

Prochlorperazine (Compazine) is an antiemetic, antipsychotic, and anxiolytic drug that inhibits the dopamine receptors known as dopaminergic D₂ receptors in the central nervous system.

Dopamine is an organic chemical involved in the transmission of instructions between neurons to control movement and reward-motivated behavior, such as pleasure, craving, decision making based on rewards, associative learning (learning new things), and short-term memory [16].

3.2.7. What Is Promethazine?

Promethazine (Phenergan) is an antihistaminic, antiemetic, and antipsychotic drug that mainly blocks H1 receptors, and therefore, prevents their activation by histamine. It has also a moderate anticholinergic activity.

Conclusion

Vertigo can be physiologic such as motion sickness; however, it can also be caused by disorders that require antivertigo drugs.

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