antiemetics

Antiemetics are medications used to prevent or treat nausea and vomiting. They act on central and peripheral pathways involved in emesis, including the chemoreceptor trigger zone, the vomiting center, the vestibular system, and the gastrointestinal tract.

Major classes include dopamine antagonists (for example metoclopramide, prochlorperazine) that block D2 receptors in the chemoreceptor trigger zone; serotonin 5-HT3 antagonists (ondansetron, granisetron, palonosetron) that block 5-HT3 receptors in the gut and CTZ; neurokinin-1 (NK1) receptor antagonists (aprepitant, netupitant) that inhibit substance P signaling; antihistamines (dimenhydrinate, meclizine, promethazine) and anticholinergics (scopolamine) that reduce vestibular input; prokinetic agents (metoclopramide and related drugs) that enhance gastric emptying; corticosteroids such as dexamethasone as adjuncts; and, in some settings, cannabinoids (dronabinol, nabilone) for antiemetic and appetite effects.

Indications include postoperative nausea and vomiting, chemotherapy- and radiotherapy-induced nausea and vomiting, motion sickness, gastroenteritis, and hyperemesis gravidarum. Efficacy and choice depend on the underlying cause, patient factors, and risk of adverse effects.

Combination therapy is common, particularly for high-risk chemotherapy regimens. A typical regimen may combine an NK1 antagonist, a 5-HT3 antagonist, and dexamethasone; alternatives exist based on tolerability and contraindications. Dosing and route depend on the drug, with oral, intravenous, and other options available for some agents.

Adverse effects vary by class: QT prolongation with certain 5-HT3 antagonists; extrapyramidal symptoms with dopamine antagonists; drowsiness with antihistamines; anticholinergic effects with scopolamine or some antihistamines; and potential drug interactions. Safety considerations include use in pregnancy, pediatrics, and the elderly, as well as specific cardiac or electrolyte considerations.