In Vitro: Dihydrotachysterol is effective in the elevation of serum calcium by stimulating intestinal calcium absorption and mobilizing bone calcium in the absence of parathyroid hormone and of functioning renal tissue. Dihydrotachysterol also increases renal phosphate excretion.
In Vivo: Dihydrotachysterol is a potent synthetic vitamin D analogue that is widely available but more expensive than vitamin D2. It has an onset of action and half-life between those of vitamin D2 and calcitriol. Dihydrotachysterol (initially given at 0.03 to 0.08 mg/kg/day for 2 to 3 days. The final dosages range from 0.004 to 0.04 mg/kg/day) is useful for the treatment of hypoparathyroidism.