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Antiemetic Medications

Editor: Anup Kasi Updated: 9/26/2022 5:56:47 PM


Nausea is a commonly encountered symptom in healthcare, one that is difficult for any patient. Causes may be as simple as the body's defense against an ingested toxin, to a complex association set of signals activated by motion, medications, anesthesia, position, stress, pregnancy, psychiatric disorder, and/or fear. Multiple or single neurohumoral pathways may be involved. Indications for the treatment of symptoms require astute evaluation by the treating provider. Therapy to treat chronic nausea stemming from chemotherapeutic agents and doses will vary from the treatment of postoperative nausea (a relatively common side effect of general anesthesia) and vomiting.[1] Acute onset nausea/emesis is more likely related to a defined insult or problem and may require a minimal or short duration of treatment. Chronic nausea is more likely to be multi-factorial, necessitate more prolonged therapy, and might be more challenging to treat. No rule of thumb can be applied when treating nausea. Empiric treatment of nausea in the absence of a clear diagnosis is typically well-tolerated and may result in a significant benefit to the patient. Practitioners should be wary of overlooking surgical emergencies such as small bowel obstructions, perforated viscus, and acute appendicitis, among others. Pregnancy merits consideration in women of child-bearing age.[2][3]

Mechanism of Action

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Mechanism of Action

There are multiple pathways and causes of nausea and vomiting. Specific areas in the brain include the area postrema in the floor of the fourth ventricle, the nucleus tractus solitarius in the medulla, and various motor nuclei that make up a central pattern generator.[4] A complex interaction of vagal afferents and efferents to the cortex, hypothalamus, and limbic regions also plays a role in how the brain perceives nausea.[5] Multiple chemoreceptors are involved in these pathways, including the muscarinic M1, dopaminergic D2, serotonin 5-HT3, neurokinin-1, and histamine H1. As such, most of the anti-emetics can broadly fit into the following classes based on the mechanism of action:

  1. Serotonin-receptor antagonists
  2. Glucocorticoids
  3. Anticholinergics
  4. Neurokinin-receptor antagonists (substance-P)
  5. Dopamine receptor antagonists
  6. Cannabinoids
  7. Antihistamines
  8. Other


The setting and clinical presentation will dictate the type of medication prescribed, the dosing, and the route of administration. A careful review of the symptoms and past medical history, allergies, and prior exposure to/uses of these medications will lead to a better outcome for the patient.

Serotonin-receptor antagonists: Ondansetron, granisetron, dolasetron, palonosetron. The mechanism of action is to block serotonin from interacting with the 5-HT3 receptor. Of these, ondansetron and granisetron are the most frequently encountered. Intravenous (IV) and oral (PO) preparations are available. Side effects include headache, dizziness, and constipation. The most worrisome side effect is QTc-prolongation, and clinicians should avoid these medications in patients with known prolonged QTc.

Glucocorticoids: The mechanism of action is not clearly understood. Possible mechanisms are changes in the blood-brain barrier and decrease the synthesis of prostaglandin messengers. Dexamethasone has been the topic of extensive study in chemotherapy and the prevention of postoperative nausea and vomiting literature. Side effects are mild when used short-term and include insomnia, excitation, and mood changes. PO and IV formulations are available.[6][7]

Anticholinergics: Scopolamine is the most commonly encountered medication in this class. It works by antagonizing the M1 muscarinic receptor. It is predominantly used to treat motion sickness or prophylactically in the perioperative setting. Side effects are typically mild but include dry mouth, vision changes, or drowsiness. The administration is transdermal.[8]

Neurokinin receptor antagonists: Aprepitant (PO) and fosaprepitant (IV) highlight this class of medications that involve antagonism of the NK-1 receptor, preventing the release of substance-P, which is an inducer of vomiting. As with many medications, side effects include headaches and dizziness, but published case reports note significant hypersensitivity reactions, including anaphylaxis and anaphylactic shock.[9]

Dopamine receptor antagonists: Phenothiazines antagonize the D2 receptor, most notably in the area postrema in the brain. Prochlorperazine and chlorpromazine are examples of this class of medication. IV, PO, and rectal (PR) formulations are available. Side effects include dizziness, headache, and extrapyramidal symptoms, including dystonia and tardive dyskinesia.[10]

Butyrophenones: These agents also work to antagonize the D2 receptor. Droperidol and Haloperidol have proven to be very efficacious anti-emetics, but due to their side effect profiles, they have fallen out of favor in many environments. Intramuscular (IM) and IV are effective routes of administration. In addition to more typical side effect profiles, these medications can cause dose-dependent QTc prolongation and require caution in those with known or suspected QTc prolongation.

Benzamides: Agents in this drug class antagonize the D2 receptor at low doses but also antagonizes the 5-HT3 receptor at higher doses. Metoclopramide is the most common medicine in this class and is typically used as a pro-motility agent to reduce nausea and vomiting. PO and IV formulations are available. This medication can cross the blood-brain barrier. As with other dopamine antagonists, this medication can cause dystonia, tardive dyskinesia, and akathisia. An FDA “Boxed” warning cautions against repeated and long-term use as it can cause irreversible tardive dyskinesia.

Cannabinoid therapy: This is relatively new and somewhat controversial. Nabilone and dronabinol have been studied and show some benefit, though significant side-effects such as vertigo, hypotension, and dysphoria have limited their use in some populations. IV and PO formulations are available.[6]

Antihistamines: These drugs act to antagonize the histamine (H1, H2) receptors.  Diphenhydramine, meclizine, promethazine are common medications in this class. They are widely available, generally well-tolerated, and PO, IV, IM, PR formulations are available. Sedation is a widely reported, common side effect.[11][12]

Adverse Effects

Generally, anti-emetic medications are well tolerated. As indicated above, side effects range from more common (mild headaches and dizziness) to rare (anaphylaxis, hypersensitivity.) The list of all side effects is beyond the scope of this document, and the practitioner should review all possible side effects (common and uncommon) before prescribing these medications. However, as noted, extrapyramidal symptoms to including tardive dyskinesia, akathisia, and dystonia, are well described. QTc prolongation and subsequent Torsades de Pointes can also be a life-threatening complications and should be considered when prescribing these medications.[13]


Contraindications will vary based on class and mechanism of medication:

  1. Serotonin-receptor antagonists:  Known hypersensitivity. Consider another class if the patient has prolonged QTc.[14] There are reports of serotonin syndrome, particularly when used in conjunction with SSRIs, selective norepinephrine serotonin reuptake inhibitors (SNRIs), mirtazapine, monoamine oxidase inhibitors(MAOIs), and other medications that modulate serotonin concentrations.
  2. Glucocorticoids: Hypersensitivity, systemic fungal infections.
  3. Anticholinergics: Known hypersensitivity, narrow-angle glaucoma
  4. Neurokinin-receptor Antagonists (Substance-P): Known hypersensitivity
  5. Dopamine receptor antagonists: Known hypersensitivity, use in children younger than 2, or weighing less than 9 kg. Consider avoiding medication in comatose patients or those with depressed Glasgow coma scale, Parkinson disease, affective disorders, or those already being treated with drugs in this class.
  6. Cannabinoids: Known hypersensitivity
  7. Antihistamines: Known hypersensitivity


Monitoring considerations will be dependent on the clinical environment and patient presentation. It is not typical to measure or use blood concentrations of any of these medications. Patient-specific monitoring relating to side effects will be specific to the patient the drug received.

Enhancing Healthcare Team Outcomes

An interprofessional team approach to antiemetics is the best course of action. As described above, nausea and vomiting is a common symptom and part of a complex pathway. Selecting the appropriate treatment option will require coordination across all areas of healthcare to include nurses, clinicians (MDs, DOs, NPs, PAs), nursing staff, pharmacists, and other health professionals. The prescriber would do well to include the pharmacist during agent selection and have the pharmacist perform thorough medication reconciliation as well as verify dosing and duration. The nursing staff can provide counsel on administration, warn about potential side effects (reinforced by the pharmacist), and answer patient questions. They can also verify therapeutic effectiveness on follow-up visits. This interprofessional team methodology will benefit the patient by increasing positive outcomes and minimizing adverse effects. [Level 5]

The current level of evidence for treatment varies for each class and specific drug. Some medications have been thoroughly tested through RCTs, sometimes alone, and sometimes in conjunction with other therapies. Other medications, for example, cannabinoids, lack an in-depth level of testing and investigation. Interprofessional teams and thoughtful, appropriate prescribing methods will increase patient safety and improve outcomes.



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