## Dexmedetomidine: α₂-Selective Agonist **Key Point:** Dexmedetomidine is a highly selective α₂-adrenergic agonist (α₂:α₁ selectivity ratio ~1600:1) that produces sedation, analgesia, and anxiolysis without respiratory depression. ### Mechanism of Action 1. Binds to presynaptic α₂ receptors in the locus coeruleus (brainstem) 2. Inhibits noradrenaline release → sedation and analgesia 3. Also activates postsynaptic α₂ receptors → vasoconstriction and analgesia ### Clinical Uses - Sedation in ICU and operating theatre - Adjunct to general and regional anaesthesia - Reduces opioid and volatile anaesthetic requirements - Maintains airway reflexes (no respiratory depression) **High-Yield:** Unlike other sedatives (propofol, benzodiazepines), dexmedetomidine does NOT cause respiratory depression — a major advantage in anaesthetic practice. ### Comparison Table: α-Agonists | Drug | Receptor Selectivity | Clinical Use | Key Feature | | --- | --- | --- | --- | | **Dexmedetomidine** | α₂ >> α₁ | Sedation, analgesia | No respiratory depression | | **Phenylephrine** | α₁ >> α₂ | Vasoconstriction, hypertension | Pure α₁ agonist | | **Dobutamine** | β₁ > β₂ | Inotropic support | Increases cardiac output | | **Isoproterenol** | β₁ = β₂ | Bronchospasm, bradycardia | Non-selective β agonist | [cite:KD Tripathi 8e Ch 9]
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