Treatment of Renal Osteodystrophy With 25-Hydroxycholecalciferol

Vitamin D₃is converted by a liver enzyme system, calciferol-25-hydroxylase, to 25-hydroxycholecalciferol (25-HCC), the active hormonal form of the vitamin. This hydroxylase is feedback inhibited by 25-HCC, and probably represents an important physiologic control step for active vitamin D. The 25-HCC is further converted in intestine, kidney, and bone to two more polar metabolites which probably represent the metabolically active form of vitamin D₃. Evidence has been presented that in uremia, excessive metabolism of vitamin D results in low plasma levels of 25-HCC. In chronically uremic rats, 25-HCC is at least one hundredfold more effective than vitamin D₃in restoring calcium absorption. In uremics, treatment with 10,000 international units (IU) of 25-HCC/day, improves calcium absorption, increases urinary and plasma calcium and decreases plasma alkaline phosphatase. Thus, 25-HCC may be the drug of choice in bone disease of uremia.