How does clonidine exert its action?

  • Selective agonist at presynaptic alpha-2 adrenoceptors:
    • Less selective than dexmedetomidine with ratio of alpha-1:alpha-2 1:200
    • Acts particularly on the locus coeruleus in the floor of the fourth ventricle, producing depression of thalamic transmission to the cerebral cortex
    • Primarily responsible for sedation, anxiolysis and analgesia
    • Reduce sympathetic outflow resulting in hypotension and bradycardia
  • Some activity at alpha-1 receptors:
    • Produces vasoconstriction at higher doses
  • Some activity at imidazole receptors:
    • Produces centrally mediated hypotension