Kinetics of serum 1,84 iPTH after high dose of calcitriol in uremic patients.

The temporal relation between oral administration of calcitriol and the nadir of PTH concentration is important for selecting optimal schedules of administration of calcitriol in the treatment of secondary hyperparathyroidism. To further assess this issue we examined 9 patients with preterminal renal failure (3 females, 6 males; median age 58.0 years, range 47-64, median S-Crea 4.8 mg/dl, range 3.7-6.8) with elevated baseline concentrations of 1,84 iPTH (median 46.0 pmol/l, range 18-100). After ingestion of a single oral dose of 2.0 micrograms calcitriol a transient rise in 1,25(OH)2D3 levels was seen with a peak at 6 h (from 20 pg/ml; 14-52 to 43 pg/ml; 35-102). 1,84 iPTH levels did not significantly change in the first 24 h, but were decreased significantly (p 0.01) 48 h after a single oral dose of calcitriol, the time to reach nadir varying from 24 to 96 hours. The percent decrease wa highest in patients with the highest baseline concentrations of 1,84 iPTH. Median 1,84 iPTH levels continued to remain below baseline at 48 h (25.0 pmol/l), 72 h (24.0 pmol/l) and 96 h (24.0 pmol/l) after oral calcitriol. A modest increase of S-Ca was noted which was not statistically significant. We conclude that 1. a single dose of oral calcitriol causes a delayed but long-lasting decrease of 1,84 iPTH, 2. decreased 1,84 iPTH levels persist despite return of calcitriol concentrations to baseline levels and 3. 1,84 iPTH may remain below baseline for more than 96 h.