A 34-year-old man undergoing awake fibreoptic intubation receives dexmedetomidine infusion. He becomes calm and drowsy but arouses readily when spoken to, and his respiratory rate and tidal volume remain unchanged. Which mechanism best accounts for this sedation profile?
- A Agonism at pontine alpha-2 receptors, decreasing locus coeruleus noradrenergic output with preservation of respiratory drive ✓
- B Enhanced GABA-A receptor activity identical to propofol, sparing medullary centres
- C Antagonism of NMDA receptors producing dissociative sedation
- D Activation of mu-opioid receptors at subanalgesic concentrations
Correct answer: A. Agonism at pontine alpha-2 receptors, decreasing locus coeruleus noradrenergic output with preservation of respiratory drive
Explanation
Dexmedetomidine is a highly selective alpha-2 agonist acting on pontine and locus coeruleus alpha-2B receptors, reducing noradrenergic firing and producing sedation resembling natural sleep, from which patients are easily roused. Because it lacks GABA-B or opioid activity, respiratory drive is essentially preserved, which distinguishes it from benzodiazepines, propofol and opioids. This unique arousable sedation without respiratory depression is its defining clinical feature.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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