Vitamin D3 (Cholecalciferol) is a fat-soluble secosteroid hormone essential for calcium and phosphate homeostasis, bone mineralization, and numerous non-skeletal functions. In the Indian context, widespread deficiency due to factors like skin pigmentation, cultural clothing, dietary habits, and limited sun exposure makes it a critical therapeutic and prophylactic agent. It is available as a nutritional supplement and prescription medicine in various oral and parenteral formulations.
Adult: **Deficiency Treatment:** 60,000 IU once weekly for 8-12 weeks, followed by maintenance (e.g., 60,000 IU monthly or 1000-2000 IU daily). **Prevention:** 400-1000 IU daily or 60,000 IU once every 2-3 months. **Osteoporosis:** 800-2000 IU daily as adjunct.
Note: Take oral capsules/tablets with a meal containing fat (e.g., milk, curd, nuts) to enhance absorption. Oral solution drops can be placed directly on the tongue or mixed with a small amount of milk/food. Intramuscular injections are administered deep IM, typically in the gluteal region.
Vitamin D3 is a prohormone. It is converted to 25(OH)D in the liver and then to the active hormone 1,25(OH)2D in the kidneys. 1,25(OH)2D binds to the Vitamin D Receptor (VDR), a nuclear transcription factor. The VDR-Retinoid X Receptor (RXR) complex binds to Vitamin D Response Elements (VDREs) in target genes, modulating their expression.
Pregnancy: Category A/C (dose-dependent). Deficiency is common and should be treated. Daily doses up to 4000 IU are considered safe. High-dose regimens should be under supervision. Essential for fetal skeletal development.
Driving: No known effects on driving ability. Drowsiness is a rare side effect.
| Thiazide Diuretics (e.g., Hydrochlorothiazide) | Increased risk of hypercalcemia due to reduced renal calcium excretion. | Major |
| Systemic Corticosteroids (e.g., Prednisolone) | May reduce calcium absorption and antagonize Vitamin D effects. | Moderate |
| Anticonvulsants (Phenobarbital, Phenytoin, Carbamazepine) | Induce hepatic CYP450 enzymes, increasing metabolism of Vitamin D to inactive compounds, leading to lower 25(OH)D levels. | Moderate |
| Orlistat, Cholestyramine | Reduce absorption of fat-soluble Vitamin D. | Moderate |
| Cardiac Glycosides (Digoxin) | Hypercalcemia may potentiate digoxin toxicity and risk of arrhythmias. | Major |
| Calcium Supplements | Additive risk of hypercalcemia and hypercalciuria. | Moderate |
| Ketoconazole, Antifungals | May inhibit the enzyme CYP27B1, reducing conversion to active form. | Minor |
Same composition (Vitamin D3 (NA)), different brands: