The Pharmacokinetics of a Single Dose of Calcitriol Administered Subcutaneously in Continuous Ambulatory Peritoneal Dialysis Patients

Objectives To evaluate the kinetics of calcitriol (1,25(OH)2D3) administered subcutaneously.Study Design Calcitriol kinetics and efficacy after subcutaneous administration were studied in 13 CAPD patients with varying degrees of increased plasma levels of parathyroid hormone (i-PTH). A single dose of 2 μg of calcitriol was administered subcutaneously, and its serum levels at baseline and after 1,2,6,12, and 24 hours were determined. Plasma ionized calcium and i-PTH were also determined at these periods.Results Serum calcitriol levels reached peak levels of 60 and 70 pg/mL at 1 and 2 hours after administration, respectively. These levels decreased thereafter, but remained above baseline values during 24 hours. The mean value of the area under the curve (AUC) was 809±226 pg/mL/hour. Plasma i-PTH levels showed a slight decrease after 1 and 2 hours, returning to baselime levels after this period. Plasma ionized calcium did not show significant changes during the study. A slight pain at the site of injection was mentioned by some patients.Conclusions The subcutaneous route for calcitriol administration achieves theoretically adequate plasma levels in continuous ambulatory peritoneal dialysis (CAPD) patients. This is important when paremteral administration of calcitriol is considered in the treatment of secondary hyperparathyroidism.