Clonidine Alpha-2 Agonist — FRCA Primary MCQ
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Correct answer: E — Alpha-2 adrenergic receptor
Clonidine is principally a centrally acting alpha-2 adrenergic receptor agonist. Alpha-2 receptors couple to Gi/o proteins, inhibiting adenylyl cyclase and reducing neuronal transmitter release. Central activation reduces sympathetic outflow, causing reductions in heart rate and arterial pressure; relevant anaesthetic effects include sedation, analgesic-sparing activity and reduced volatile anaesthetic requirement. Clonidine also binds imidazoline receptors, so option C describes an additional target but not the principal adrenergic receptor requested. Beta-1 stimulation would increase cardiac rate and contractility, while alpha-1 stimulation predominantly causes vasoconstriction. Muscarinic M2 receptors mediate parasympathetic cardiac effects and are not clonidine's target.
Reference: electronic Medicines Compendium, Clonidine hydrochloride 50 micrograms/5 ml Oral Solution, Summary of Product Characteristics, section 5.1 Pharmacodynamic properties, 2026. https://www.medicines.org.uk/emc/product/101738/smpc