The hydrochloride salt form of clonidine, an imidazoline derivate and centrally-acting alpha-adrenergic agonist as well as antagonist with antihypertensive activity. Clonidine hydrochloride binds to and stimulates central alpha-2 adrenergic receptors, thereby decreasing sympathetic outflow to the heart, kidneys, and peripheral vasculature. The reduction in sympathetic outflow, leads to decreased peripheral vascular resistance, decreased blood pressure, and decreased heart rate. or A drug used to treat certain types of acute lymphoblastic leukemia in children. It is also being studied in the treatment of other types of cancer. Clofarabine is a type of nucleoside analog. Also called Clolar.