Paricalcitol (marketed by Abbott Laboratories under the trade name Zemplar) is a drug used for the prevention and treatment of secondary hyperparathyroidism (excessive secretion of parathyroid hormone) associated with chronic renal failure. Chemically, it is 19-nor-1,25-(OH)₂-vitamin D₂ or 19-nor-1,25-dihydroxyvitamin D₂, being an analog of 1,25-dihydroxyergocalciferol, the active form of vitamin D₂.