Antiemetics
Antiemetics are grouped by the receptor they block along the emetic pathway, and correct use is a matching exercise: identify the trigger (chemotherapy, postoperative, vestibular, gastroparesis, or pregnancy) and select the class built for that pathway, most often a 5-HT3 antagonist, a D2 antagonist, an NK1 antagonist, or an antihistamine/anticholinergic, layered with dexamethasone for chemotherapy-induced disease.
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What this article covers
- Overview
Definition: antiemetics are drug classes that block distinct receptors along the vomiting pathway; rational selection matches the class to the mechanism driving the patient's nausea rather than reaching for one default agent.
- Epidemiology
Chemotherapy-induced nausea and vomiting: without prophylaxis, highly emetogenic regimens (cisplatin, anthracycline-cyclophosphamide, dacarbazine, mechlorethamine, streptozocin) cause vomiting in…
- Risk factors
QT-prolonging comorbidity or drugs: congenital long-QT syndrome, bradyarrhythmia, uncorrected hypokalemia or hypomagnesemia, heart failure, or another QT-prolonging drug raises torsades risk with 5-HT3 antagonists.
- Pathophysiology
Vomiting is a coordinated brainstem reflex: afferents from the gut, chemoreceptor trigger zone, vestibular apparatus, and cortex converge on brainstem circuitry that drives emesis.
- Clinical features
Chemotherapy-induced nausea and vomiting: acute (within 24 hours, serotonin/gut-mediated) and delayed (after 24 hours, substance P/NK1-mediated) phases; anticipatory nausea can develop after poorly controlled early cycles.
- Differential diagnosis
Chemotherapy or radiotherapy exposure: drives acute and delayed CINV; treat with the emetogenic-risk-based regimen rather than a single agent.
- Diagnosis
Identify the trigger first, because it sets which receptor pathway to block: classify as chemotherapy/radiotherapy (and its emetogenic tier), postoperative, vestibular/motion, gastroparesis…
- Management
Chemotherapy-induced nausea and vomiting, high emetic risk: give a four-drug regimen before chemotherapy.
- Complications
Torsades de pointes: the principal serious risk of 5-HT3 antagonists, from dose-dependent QT prolongation, most likely with high-dose IV ondansetron or an existing QT risk factor.
- Prognosis
CINV control drives chemotherapy tolerability: risk-matched prophylaxis has markedly reduced acute and delayed-phase vomiting; poor early control predicts anticipatory nausea later.
- Prevention
Match CINV prophylaxis to emetogenic risk before the first dose: four-drug for high risk, two-drug (5-HT3 antagonist plus dexamethasone) for moderate risk, single-agent for low risk, rather than treating breakthrough reactively.
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