| Ergocalciferol is vitamin D2. Ergocalciferol is a fat-soluble vitamin that regulates calcium and phosphorus metabolism. Vitamin D is important for the absorption of calcium from the stomach and for the functioning of calcium in the body. Ergocalciferol is 9. 10-secoergosta-5,7,10(19),22-tetraen-3- 01,(3b,5Z,7E,22E)-, (C28H44O) with a molecular weight of 39665. Ergocalciferol is a white,
colorless crystal, insoluble in water, soluble in organic solvents, and slightly soluble in vegetable oils. It is affected by air and by light. Ergosterol or provitamin d2 is found in plants and yeast and has no antiarichitic activity. Vitamin D2 is derived from fungal and plant sources. Vitamin D2 is also known as ergocalciferol.
Vitamin D is absorbed primarily in the duodenum and the overall efficiency of absorption is about 50%. In the liver, vitamin D is converted (by vitamin D-25-hydroxylase) into the highly active calcitriol (25-hydroxyvitamin D), which is transported through the body by a carrier protein. Ergocalciferol (vitamin D2) is of plant origin. Calciferol (vitamin D3) is found in animals, especially in the livers of fish. Ergocalciferol (vitamin D2) is produced by ultraviolet irradiation of a provitamin D sterol (ergosterol) which occurs in yeast and fungi. Both of these agents which have equal biologic activity are metabolized in the liver to calcifediol (25-hydroxycholecalciferol) which is then hydroxylated in the kidney to calcitriol (1,25-dihydroxycholecalciferol). Calcitriol is considered the most active form. Dihydrotachysterol is produced by synthetic reduction of ergocalciferol. Patients with chronic renal disease cannot convert calcifediol to calcitriol. Alfacalcidol (1hydroxyvitamin D3), a synthetic analogue of calcitriol, is rapidly converted in the liver to calcitriol, bypassing the renal conversion step.
Ergocalciferol is used in the treatment of refractory rickets (vitamin-D resistant rickets), familial hypophosphatemia, and hypoparathyroidism. Ergocalciferol (vitamin D2) is used to promote healthy bones and teeth, to help boost the immune system and is sometimes used in the treatment of psoriasis. Vitamin D is also administered for the treatment of lupus, pleurisy and tuberculosis of the larynx, kidneys. Vitamin D2 (ergocalciferol) is the form most often added to milk and other foods, and the form most often found in nutrition supplements. Ergocalciferol has the highest activity from the group of Vitamin D. It regulates phosphorus-calcium metabolism and the processes of ossification. It also control the absorption of phosphorus and amino acids in renal tubules. | 
