Alfacalcidol is a synthetic, active vitamin D3 analog (1α-hydroxyvitamin D3). It is a prohormone that undergoes rapid hepatic 25-hydroxylation to form its active metabolite, calcitriol (1,25-dihydroxyvitamin D3). Unlike native vitamin D, it does not require renal 1α-hydroxylation, making it effective in patients with impaired renal function. It regulates calcium and phosphate homeostasis by promoting intestinal absorption, renal reabsorption, and bone mineralization. It is a cornerstone therapy for renal osteodystrophy, hypoparathyroidism, and osteoporosis in the Indian context.
Adult: Initial dose: 0.5 mcg to 1.0 mcg once daily. Maintenance dose: 0.25 mcg to 1.0 mcg daily, adjusted based on biochemical response. For osteoporosis: 0.5 mcg to 1.0 mcg daily. For renal osteodystrophy: 0.25 mcg to 1.0 mcg daily.
Note: Administer orally, once daily, preferably with or after food to enhance absorption. Capsule/tablet should be swallowed whole with a glass of water. Avoid taking with large amounts of high-fiber foods or phytates (bran, whole grains) simultaneously, as they can reduce absorption. Maintain adequate dietary calcium intake (800-1000 mg/day) unless contraindicated.
Alfacalcidol is a direct precursor to the active hormone calcitriol. After 25-hydroxylation in the liver, it binds to the vitamin D receptor (VDR) in target tissues (intestine, bone, kidney, parathyroid glands). The VDR complex heterodimerizes with the retinoid X receptor (RXR) and binds to Vitamin D Response Elements (VDREs) in the DNA, modulating gene transcription. This increases the synthesis of calcium-binding proteins (calbindin-D) in the intestine, promoting active calcium and phosphate absorption. In bone, it stimulates osteoblast activity and mineralization. In the parathyroid glands, it suppresses the transcription of the parathyroid hormone (PTH) gene, reducing PTH secretion.
Pregnancy: Category C (US FDA). Use only if potential benefit justifies potential risk to the fetus. Animal studies show teratogenicity at high doses. Maternal hypercalcemia can lead to fetal hypercalcemia, suppression of parathyroid function, and distinctive elfin facies syndrome. Monitor maternal calcium closely.
Driving: No known effects on driving ability. However, severe hypercalcemia can cause fatigue, drowsiness, and confusion, impairing these skills.
| Thiazide Diuretics (Hydrochlorothiazide) | Increased risk of hypercalcemia due to reduced renal calcium excretion. | Major |
| Cardiac Glycosides (Digoxin) | Hypercalcemia potentiates digitalis toxicity, risk of serious cardiac arrhythmias. | Major |
| Magnesium-containing Antacids/Laxatives | Increased risk of hypermagnesemia, especially in renal failure patients. | Moderate |
| Cholestyramine, Colestipol | Reduced intestinal absorption of alfacalcidol. Administer at least 2 hours apart. | Moderate |
| Phenytoin, Phenobarbital, Carbamazepine | Increased hepatic metabolism of alfacalcidol/calcitriol, reducing efficacy. | Moderate |
| Corticosteroids (e.g., Prednisolone) | Antagonize the calcium-absorbing effect of vitamin D analogs. | Moderate |
| Ketoconazole, Itraconazole | May inhibit metabolism of vitamin D analogs, potentially increasing their effect and risk of hypercalcemia. | Moderate |
Same composition (Alfacalcidol (0.5mcg)), different brands: