Description : Alfacalcidol is an active metabolite of Vitamin D, Indication : prescribed for hypocalcaemia, hypoparathyroidism, hypophosphataemia, renal osteodystrophy, and osteomalacia. dosage : Adult- PO- The recommended starting dose is 1mcg/day. Maintenance: 0.25-1 mcg/day. Adult- IV- The recommended initial dose is 1 mcg per dialysis two to three times a week. Mechanism of action The first step involved in the activation of vitamin D3 is a 25-hydroxylation which is catalysed by the 25-hydroxylase in the liver and then by other enzymes. The mitochondrial sterol 27-hydroxylase catalyses the first reaction in the oxidation of the side chain of sterol intermediates. The active form of vitamin D3 (calcitriol) binds to intracellular receptors that then function as transcription factors to modulate gene expression. Like the receptors for other steroid hormones and thyroid hormones, the vitamin D receptor has hormone-binding and DNA-binding domains.