Falecalcitriol is an analog of calcitriol. Falecalcitriol was first approved by Pharmaceuticals and Medicals Devices Agency of Japan (PMDA) on Apr 4, 2001. It was co-developed by Taisho, Dainippon Sumitomo and Kissei, then marketed as Hornel by Taisho and Taisho Toyama or as Fulstan by Dainippon Sumitomo Pharma and Kissei in JP. It has a higher potency both in vivo and in vitro systems, and longer duration of action in vivo. This medicine improves bone disease and symptoms caused by shortage of vitamin D, etc. It also prompts calcium absorption to supply lacked calcium and prevents bone-thinning. It is usually used to treat secondary hyperparathyroidism under maintenance dialysis, hypoparathyroidism, rickets or osteomalacia. Falecalcitriol regulates the proliferation of parathyroid cells and parathyroid hormone synthesis possibly via binding to a nuclear receptor for vitamin D (VDR). It is often not possible to administer doses high enough to sufficiently inhibit parathyroid hormones because of the risk of hypercalcemia and hyperphosphatemia.