- Metabolism: Within the liver, ergocalciferol is hydroxylated to ercalcidiol (25-hydroxyergocalciferol) by the enzyme 25-hydroxylase. Within the kidney, ercalcidiol serves as a substrate for 1-alpha-hydroxylase, yielding ercalcitriol (1,25-dihydroxyergocalciferol), the biologically active form of vitamin D2. Half Life: 19 to 48 hours (however, stored in fat deposits in body for prolonged periods).
- Uses/Sources: For use in the management of hypocalcemia and its clinical manifestations in patients with hypoparathyroidism, as well as for the treatment of familial hypophosphatemia (vitamin D resistant rickets). This drug has also been used in the treatment of nutritional rickets or osteomalacia, vitamin D dependent rickets, rickets or osteomalacia secondary to long-term high dose anticonvulsant therapy, early renal osteodystrophy, osteoporosis (in conjunction with calcium), and hypophosphatemia associated with Fanconi syndrome (with treatment of acidosis).
- Symptoms: Nausea, vomiting and diarrhea, weight loss, irritability, weakness, fatigue, lassitude, and headache.
- Treatment: The treatment of hypervitaminosis D with hypercalcemia consists in immediate withdrawal of the vitamin, a low calcium diet, generous intake of fluids, along with symptomatic and supportive treatment. Hypercalcemic crisis with dehydration, stupor, coma, and azotemia requires more vigorous treatment. The first step should be hydration of the patient. Intravenous saline may quickly and significantly increase urinary calcium excretion. A loop diuretic (furosemide or ethacrynic acid) may be given with the saline infusion to further increase renal calcium excretion. Other reported therapeutic measures include dialysis or the administration of citrates, sulfates, phosphates, corticosteroids, EDTA (ethylenediaminetetraacetic acid), and mithramycin via appropriate regimens. (L1712)
- Route of Exposure: Oral, readily absorbed.
- Carcinogenicity: No indication of carcinogenicity to humans (not listed by IARC).
- Toxicity: LD<sub>50</sub> = 23.7 mg/kg (Orally in mice); LD<sub>50</sub> = 10 mg/kg (Orally in rats ).
Mechanism of Action
|Target Name||Mechanism of Action||References|
|Nuclear receptor subfamily 1 group I member 2||
25-hydroxyvitamin D-1 alpha hydroxylase, mitochondrial
Vitamin D3 receptor
Vitamin D 25-hydroxylase
|Vitamin D2 is the form of vitamin D most commonly added to foods and nutritional supplements. Vitamin D2 must be transformed (hydroxylated) into one of two active forms via the liver or kidney. Once transformed, it binds to the vitamin D receptor that then leads to a variety of regulatory roles. Vitamin D plays an important role in maintaining calcium balance and in the regulation of parathyroid hormone (PTH). It promotes renal reabsorption of calcium, increases intestinal absorption of calcium and phosphorus, and increases calcium and phosphorus mobilization from bone to plasma. Vitamin D2 and its analogs appear to promote intestinal absorption of calcium through binding to a specific receptor in the mucosal cytoplasm of the intestine. Subsequently, calcium is absorbed through formation of a calcium-binding protein.||