Hello-D/Hello-D 2000 Mechanism of Action

Pharmacology: Pharmacodynamics: Vitamin D is considered a hormone, although not a natural human hormone. Biologically active vitamin D metabolites control the intestinal absorption of dietary calcium, the tubular reabsorption of calcium by the kidney, and in conjunction with parathyroid hormone (PTH), the mobilization of calcium from the skeleton. They act directly on bone cells (osteoblasts) to stimulate skeletal growth and on the parathyroid glands to suppress PTH synthesis and secretion. Vitamin D is also involved in magnesium metabolism.
Pharmacokinetics: Absorption: Vitamin D₃ is absorbed more rapidly and more completely than vitamin D₂. Bile is essential for adequate absorption. Absorption is reduced in liver or biliary disease. Calcifediol's maximum concentration (C_max) is 4 hours following oral administration.
Distribution: Stored chiefly in the liver, vitamin D is also found in fat, muscle, skin, and bones. In plasma, it is bound to α-globulins and albumin.
Metabolism: Within the liver, cholecalciferol is hydroxy­lated to calcifediol (25-hydroxycholecalciferol) by the enzyme 25-hydroxylase. Within the kidney, calcifediol serves as a substrate for 1-alpha-hydroxylase, yielding calcitriol (1, 25- dihydroxycholecalciferol), the biologically active form of vitamin D.
Excretion: The primary route of vitamin D excretion is in the bile; only a small percentage is found in the urine.