Antiemetic – Mechanism, Uses and Side Effects
An antiemetic is a medication used to prevent or treat nausea and vomiting. It is commonly used for motion sickness, chemotherapy side effects, or postoperative nausea.
Things worth knowing about "Antiemetic"
An antiemetic is a medication used to prevent or treat nausea and vomiting. It is commonly used for motion sickness, chemotherapy side effects, or postoperative nausea.
What is an Antiemetic?
An antiemetic is a type of medication specifically designed to prevent or relieve nausea and vomiting (emesis). The term comes from the Greek words anti (against) and emein (to vomit). Antiemetics are among the most widely used drug classes in clinical medicine and are available both by prescription and over the counter, depending on the active ingredient and intended use.
Indications
Antiemetics are used across a wide range of conditions and clinical situations that involve nausea and vomiting:
- Motion sickness (kinetosis)
- Chemotherapy-induced nausea and vomiting (CINV)
- Postoperative nausea and vomiting (PONV)
- Pregnancy-related nausea and vomiting (morning sickness, hyperemesis gravidarum)
- Gastroenteritis (stomach flu)
- Migraine-associated nausea
- Medication-induced nausea (e.g., from opioids or other drugs)
Mechanism of Action
The vomiting reflex is controlled by the vomiting center in the brainstem and by the chemoreceptor trigger zone (CTZ) located in the area postrema. Antiemetics act on various receptor types to suppress this reflex. The specific mechanism depends on the pharmacological class of the drug.
Dopamine Receptor Antagonists
Agents such as metoclopramide and domperidone block dopamine D2 receptors in the CTZ and gastrointestinal tract. They also promote gastric emptying (prokinetic effect), making them particularly useful for nausea associated with gastroparesis or postoperative states.
Serotonin 5-HT3 Receptor Antagonists
Ondansetron, granisetron, and related compounds block serotonin receptors in the gut and central nervous system. They are highly effective against chemotherapy-induced nausea and are a cornerstone of CINV management.
NK1 Receptor Antagonists
Aprepitant and related drugs block neurokinin-1 receptors, which respond to substance P. These are used primarily in combination regimens for highly emetogenic chemotherapy protocols.
Antihistamines
Agents such as dimenhydrinate and meclizine block histamine H1 receptors and reduce activity in the vestibular system. They are most effective for motion sickness and vestibular-related nausea.
Corticosteroids
Dexamethasone is frequently used in combination with other antiemetics, especially for chemotherapy-related nausea prevention. Its exact antiemetic mechanism is not yet fully understood.
Cannabinoids
Synthetic cannabinoids such as nabilone and dronabinol are reserved for patients with CINV that does not respond adequately to other antiemetic treatments.
Dosage and Administration
The appropriate dosage and administration route depend on the underlying cause of nausea, the severity of symptoms, and the individual patient profile including age and medical history. Antiemetics are available in several forms:
- Tablets and capsules (oral)
- Orally disintegrating tablets (sublingual or buccal)
- Suppositories (rectal)
- Injectable solutions (intravenous or intramuscular)
- Transdermal patches (e.g., scopolamine for motion sickness)
Side Effects
Side effects vary depending on the drug class used. Common adverse effects include:
- Dopamine antagonists: Drowsiness, extrapyramidal symptoms (e.g., involuntary movements), elevated prolactin levels
- 5-HT3 antagonists: Headache, constipation, QT interval prolongation on ECG
- Antihistamines: Sedation, dry mouth, dizziness
- NK1 antagonists: Hiccups, fatigue, drug interactions
- Corticosteroids: Generally well tolerated short-term; prolonged use may raise blood glucose and cause systemic effects
Important Notes
Antiemetics should always be used under medical guidance, especially in pregnancy, in children, and in patients with cardiovascular conditions. Some antiemetics may impair the ability to drive or operate machinery. Persistent or unexplained nausea and vomiting should always be evaluated by a healthcare professional to identify and treat the underlying cause.
References
- Roila F. et al. - ESMO Clinical Practice Guidelines: Prevention of chemotherapy- and radiotherapy-induced nausea and vomiting. Annals of Oncology, 2016; 27 (Suppl 5): v119-v133
- Gan T.J. et al. - Fourth Consensus Guidelines for the Management of Postoperative Nausea and Vomiting. Anesthesia and Analgesia, 2020; 131(2): 411-448
- Katzung B.G. (Ed.) - Basic and Clinical Pharmacology, 15th Edition, McGraw-Hill Education (2021)
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