Antiemetics

• Antiemetics are drugs that prevent or control nausea and vomiting by acting on central or peripheral pathways.

Definition of Antiemetics

• Drugs used to prevent or control nausea and vomiting due to various causes (motion sickness, chemotherapy, infections, etc.)

Classes of Antiemetic Drugs

1. Dopamine (D₂) Receptor Antagonists

• Examples: Metoclopramide, Domperidone
• Mechanism: Block D₂ receptors in CTZ
• Use: Vomiting due to GI causes, post-op nausea
• Metoclopramide also has prokinetic action
• Side Effects: Extrapyramidal symptoms (EPS), especially in children

2. 5-HT₃ (Serotonin) Receptor Antagonists

• Examples: Ondansetron, Granisetron
• Mechanism: Block 5-HT₃ receptors in CTZ and GI tract
• Use: Chemotherapy-induced nausea and vomiting (CINV), post-op nausea
• Note: Very effective and well-tolerated

3. H₁-Antihistamines

• Examples: Promethazine, Diphenhydramine, Meclizine
• Mechanism: Block H₁ receptors in vestibular system
• Use: Motion sickness, vertigo
• Side Effects: Sedation, dry mouth

4. Anticholinergics (M1 Blockers)

• Example: Hyoscine (Scopolamine)
• Mechanism: Block muscarinic receptors in vestibular pathway
• Use: Motion sickness (patches/tablets)
• Side Effects: Dry mouth, drowsiness, blurred vision

5. Neurokinin-1 (NK1) Receptor Antagonists

• Example: Aprepitant
• Mechanism: Block substance P binding at NK1 receptors in brain
• Use: CINV (in combination with 5-HT₃ blockers and steroids)
• Note: Newer, used in severe or refractory cases

6. Corticosteroids

• Example: Dexamethasone
• Mechanism: Unclear; anti-inflammatory and central effect
• Use: Part of combination for CINV and post-op nausea

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