THE PHARMACOKINETICS OF A SINGLE-DOSE OF CALCITRIOL ADMINISTERED SUBCUTANEOUSLY IN CONTINUOUS AMBULATORY PERITONEAL-DIALYSIS PATIENTS

Objective: To evaluate the kinetics of calcitriol (1,25(OH)2D3) admini stered subcutaneously. Study Design: Calcitriol kinetics and efficacy after subcutaneous administration were studied in 13 CAPD patients wit h varying degrees of increased plasma levels of parathyroid hormone (i -PTH). A single dose of 2 mug of calcitriol was administered subcutane ously, and its serum levels at baseline and after 1, 2,6,12, and 24 ho urs were determined. Plasma ionized calcium and i-PTH were also determ ined at these periods. Results: Serum calcitriol levels reached peak l evels of 60 and 70 pg/mL at 1 and 2 hours after administration, respec tively. These levels decreased thereafter, but remained above baseline values during 24 hours. The mean value of the area under the curve (A UC) was 809+/-226 pg/mL/hour. Plasma i-PTH levels showed a slight decr ease after 1 and 2 hours, returning to baseline levels after this peri od. Plasma ionized calcium did not show significant changes during the study. A slight pain at the site of injection was mentioned by some p atients. Conclusions: The subcutaneous route for calcitriol administra tion achieves theoretically adequate plasma levels in continuous ambul atory peritoneal dialysis (CAPD) patients. This is important when pare nteral administration of calcitriol is considered in the treatment of secondary hyperparathyroidism.