antiemètics

Antiemetics are medicines used to prevent or treat nausea and vomiting. They work by interfering with signals to the vomiting center in the brain, the chemoreceptor trigger zone, or by blocking pathways in the gut and vestibular system that trigger nausea. They are commonly used for postoperative nausea and vomiting (PONV), chemotherapy-induced nausea and vomiting (CINV), motion sickness, gastroenteritis, and pregnancy-related nausea, among other conditions.

The major classes include dopamine receptor antagonists such as metoclopramide and prochlorperazine; these block D2 receptors in the CTZ and gut, but can cause extrapyramidal symptoms and sedation. Serotonin 5-HT3 receptor antagonists (ondansetron, granisetron, palonosetron) block 5-HT3 receptors in the gut and CTZ, are effective for CINV and PONV, but may prolong QT interval in some patients. Neurokinin-1 receptor antagonists (aprepitant, rolapitant) block substance P signaling and are often used with steroids for CINV; they can interact with cytochrome P450 enzymes. Antihistamines (dimenhydrinate, meclizine, diphenhydramine) provide relief for motion sickness and include sedative effects. The antimuscarinic scopolamine, delivered by a transdermal patch, also helps motion sickness and postural nausea, with dry mouth and cognitive effects as potential side effects.

Adjuncts and safety considerations include the use of corticosteroids such as dexamethasone in multi-drug regimens and benzodiazepines for anticipatory nausea. Choice of agent depends on the underlying cause, patient factors, and potential contraindications. Common adverse effects vary by class: QT prolongation with 5-HT3 antagonists; extrapyramidal symptoms with dopamine antagonists; sedation with antihistamines; anticholinergic effects with scopolamine. Drug interactions and organ function (liver, kidney) may influence dosing and selection.