### Date : 2024-06-24 12:41 ### Topic : Antiemetics #medicine #pharmacology #ENT ---- ### Antiemetics Overview Antiemetics are medications that help prevent and treat nausea and vomiting. Each class of antiemetics works through different mechanisms and has specific cautions associated with their use. ### Classes of Antiemetics 1. **Serotonin (5-HT3) Receptor Antagonists** - **Examples:** Ondansetron, granisetron, palonosetron. - **Mechanism:** Block serotonin receptors in the central nervous system and gastrointestinal tract, which are involved in triggering nausea and vomiting. - **Uses:** Chemotherapy-induced nausea and vomiting (CINV), postoperative nausea and vomiting (PONV), and radiation therapy-induced nausea and vomiting. - **Cautions:** - **QT Prolongation:** Use with caution in patients with a history of QT prolongation or those taking other medications that prolong the QT interval. - **Constipation:** Monitor for severe constipation or bowel obstruction. - **Hypersensitivity:** Be aware of potential allergic reactions. 2. **Dopamine (D2) Receptor Antagonists** - **Examples:** Metoclopramide, prochlorperazine, promethazine. - **Mechanism:** Block dopamine receptors in the brain, particularly in the chemoreceptor trigger zone (CTZ), which is involved in the vomiting reflex. - **Uses:** General nausea and vomiting, postoperative nausea and vomiting, migraine-associated nausea. - **Cautions:** - **Extrapyramidal Symptoms:** Monitor for movement disorders such as dystonia, akathisia, and tardive dyskinesia. - **Sedation:** Can cause drowsiness; avoid in activities requiring alertness. - **Hypotension:** Watch for low blood pressure, particularly in elderly patients. 3. **Antihistamines (H1 Receptor Antagonists)** - **Examples:** Dimenhydrinate, diphenhydramine, meclizine. - **Mechanism:** Block histamine receptors in the vestibular system and brain, reducing signals that cause nausea and vomiting. - **Uses:** Motion sickness, vertigo, and mild nausea and vomiting. - **Cautions:** - **Drowsiness:** Causes sedation; caution when driving or operating heavy machinery. - **Anticholinergic Effects:** Can cause dry mouth, urinary retention, and blurred vision; use with caution in patients with glaucoma or prostatic hypertrophy. - **Interactions:** Be aware of potential interactions with other CNS depressants. 4. **Anticholinergics** - **Examples:** Scopolamine. - **Mechanism:** Block acetylcholine receptors in the vestibular system and brain, reducing vestibular input to the vomiting center. - **Uses:** Motion sickness, postoperative nausea and vomiting. - **Cautions:** - **Anticholinergic Effects:** Causes dry mouth, dizziness, blurred vision, and constipation; use cautiously in elderly patients and those with glaucoma or urinary retention. - **CNS Effects:** Can cause confusion and hallucinations, especially in elderly patients. - **Interactions:** Potential interactions with other anticholinergic medications. 5. **Neurokinin-1 (NK1) Receptor Antagonists** - **Examples:** Aprepitant, fosaprepitant. - **Mechanism:** Block NK1 receptors in the brain, which are involved in the vomiting reflex. - **Uses:** Chemotherapy-induced nausea and vomiting, often used in combination with serotonin antagonists and corticosteroids. - **Cautions:** - **Drug Interactions:** Can interact with other medications metabolized by CYP3A4; monitor for potential interactions. - **Fatigue and Dizziness:** Common side effects; monitor patients for these symptoms. - **Cost:** Can be expensive; consider cost-effectiveness for long-term use. 6. **Cannabinoids** - **Examples:** Dronabinol, nabilone. - **Mechanism:** Act on cannabinoid receptors in the brain to reduce nausea and vomiting. - **Uses:** Chemotherapy-induced nausea and vomiting, particularly when other treatments are ineffective. - **Cautions:** - **Psychotropic Effects:** Can cause euphoria, dizziness, and hallucinations; use with caution in patients with a history of psychiatric disorders. - **Abuse Potential:** Monitor for signs of misuse or dependency. - **Sedation:** Can cause drowsiness; caution when driving or operating heavy machinery. 7. **Corticosteroids** - **Examples:** Dexamethasone. - **Mechanism:** Reduce inflammation and have antiemetic effects through mechanisms not entirely understood, likely involving multiple pathways. - **Uses:** Chemotherapy-induced nausea and vomiting, postoperative nausea and vomiting, often used in combination with other antiemetics. - **Cautions:** - **Hyperglycemia:** Can elevate blood sugar levels; use with caution in diabetic patients. - **Immune Suppression:** Long-term use can suppress the immune system; monitor for signs of infection. - **Psychiatric Effects:** Can cause mood changes, insomnia, and, in rare cases, psychosis; monitor for these side effects.