Name: Dihydrotachysterol (Hytakerol, DHT)
Class: Vitamin
Mechanism: Increases intestinal absorption of calcium and phosphate. Stimulates bone resorption by facilitating effects of PTH. Stimulates renal reabsorption of calcium and phosphate. Net result = calcium, phosphate.
Absorption: Oral usu ® adequate absorption. Bile is essential for absorption.
Dist.: Stored in fat and muscle. Tightly bound to vitamin D-binding protein.
Metabolism.: Requires hydroxylation in liver for full activity.
Excretion, t½: 1° = bile.
Toxicity/S.E.s: Excess accumulation in fat/muscle, hypervitaminosis D, hypercalcemia. Drug interactions—phenytoin and phenobarbital reduce sensitivity to vit. D and/or increase rate of inactivation of calcitriol.
Utility: Treat X-linked hypophosphatemic rickets (+ phosphate salts). Treat renal osteodystrophy 2° to chronic renal disease. Treat hypoparathyroidism (+ calcium).
Special Features: Does not require kidney activation. Liver hydroxylation produces full activity. ¼ the price of calcitriol, but takes 1-2 wk. to increase serum calcium. Serum concentration not measurable.