Single-dose oral calcitriol and changes of plasma 1,84iPTH in uremic children.

Both intravenous and oral 1,25(OH)2 D3 pulse therapy are effective in decreasing iPTH in patients with chronic renal failure. In order to understand why intermittent application of calcitriol is effective, we investigated 10 children with advanced renal failure (4 female, 6 male; median age 6.5 [3-16] years; body surface area 0.58-1.57m2; CCR 7 [5-47] mL/min/1.73m2) with elevated baseline concentrations of 1,84iPTH (median 63.5 [9.4-300] pmol/L). After a standard dose of 2 micrograms calcitriol per os (equal to 1.27-3.45 micrograms/m2), serum 1,25(OH)2D3 concentrations increased. The peak concentration occurred after 6 h (3-12), and 1,25(OH)2D3 serum levels returned to baseline by 48 h. 1,84iPTH concentrations were significantly suppressed by 6-72 h. The median maximal decrease was 51.4% of baseline (22.3%-74%). The decrement was a function of baseline 1,84iPTH, but not of 1,25(OH)2D3 serum peak concentration, area under the curve, body surface area, or change in ionized serum calcium. We conclude: (i) oral 1,25(OH)2D3 has a prolonged (up to 72 h) suppressive effect on 1,84iPTH concentrations in uremic patients, and (ii) the wide interindividual variation in suppression of 1,84iPTH was not explained by the kinetics of 1,25(OH)2D3 concentration, which implies that additional factors influence the 1,84iPTH response to 1,25(OH)2D3.