Dexmedetomidine

Dexmedetomidine is a potent, highly specific **alpha-2 adrenergic agonist** used primarily as a sedative, analgesic, and preanesthetic in veterinary medicine. It is the dextrorotatory enantiomer of medetomidine, making it approximately twice as potent as the racemic mixture. **Key Clinical Features:** * **Biphasic Cardiovascular Response:** Initial peripheral vasoconstriction leads to transient hypertension and a pronounced reflex bradycardia. This is followed by a central sympatholytic effect causing normotension or mild hypotension, while bradycardia persists. * **Analgesia:** Provides excellent visceral and somatic analgesia, often synergistic with opioids (e.g., "kitty magic" or "doggie magic" protocols). * **Reversibility:** Effects can be rapidly and completely reversed using the specific alpha-2 antagonist **atipamezole**. * **Dosing:** In dogs, dosing is uniquely based on **body surface area (BSA)** rather than strictly by weight, as smaller dogs require higher per-kg doses to achieve similar sedation levels.

กลไกการออกฤทธิ์: Dexmedetomidine acts as a highly selective agonist at **pre-synaptic alpha-2 adrenergic receptors** in the central and peripheral nervous systems. * **CNS Effects:** Activation of alpha-2 receptors in the locus coeruleus → decreased norepinephrine release → profound sedation, anxiolysis, and analgesia. * **Cardiovascular Effects:** Activation of peripheral post-synaptic alpha-2B receptors in vascular smooth muscle → intense vasoconstriction → increased systemic vascular resistance (SVR) → reflex bradycardia mediated by baroreceptors. Central alpha-2A activation subsequently decreases sympathetic outflow. * **Other Effects:** Decreases GI secretions, alters intestinal motility, induces diuresis (via inhibition of ADH), and causes mild muscle relaxation.

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