The Effect of Renal Function on Changes in Circulating Concentrations of 1,25-Dihydroxycholecalciferol after An Oral Dose

1. 1,25-Dihydroxycholecalciferol [1,25-(OH)₂-D₃] was administered orally to four normal subjects and six patients with chronic renal failure not on dialysis. The serum concentration of 1,25-(OH)₂D₃ was measured by radioimmunoassay in both groups from samples taken before, and at regular intervals up to 48 h after, the oral dose.

2. The plasma half-time for the disappearance of the administered 1,25-(OH)₂D₃ was estimated by determining the time for a 50% reduction from the peak increment of the sterol. In normal subjects the calculated value ranged from 5 to 8 h compared with 18 to 44 h in uraemic patients.

3. It appears from our studies that in uraemic subjects there is impaired ability to metabolize or excrete 1,25-(OH)₂D₃.