Dihydrotachysterol is hydroxylated in the liver to 25-hydroxydihydrotachysterol, which is the major circulating active form of the drug. It does not undergo further hydroxylation by the kidney and therefore is the analogue of 1, 25-dihydroxyvitamin D. 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 contrast to parathyroid extract, dihydrotachysterol is active when taken orally, exerts a slow but persistent effect, and may be used for long periods without increasing the dosage or causing tolerance. Dihydrotachysterol is faster-acting than pharmacologic doses of vitamin D and is less persistent after cessation of treatment, thus decreasing the risk of accumulation and of hypercalcemia.

Last reviewed on RxList: 12/8/2004
This monograph has been modified to include the generic and brand name in many instances.