Pharmacology Clonidine is an imidazoline, a class of drugs that function as centrally-acting presynaptic alpha 2 agonists . Essentially clonidine acts like pushing down on the break pedal of sympathetic output thus decreasing sympathetically mediated vasoconstriction, cardiac inotropy, and chronotropy. It has rapid GI absorption and highly lipid soluble with excellent CNS penetration. Peak concentration is reached at 3 to 5 hours. [...]