19-Nor-1-alpha-25-dihydroxyvitamin D2 (Paricalcitol) safely and effectively reduces the levels of intact parathyroid hormone in patients on hemodialysis.

Paricalcitol (19-nor-1alpha-25-dihydroxyvitamin D2), a new vitamin D analog developed for the treatment of secondary hyperparathyroidism, was evaluated in three double-blind, placebo-controlled, dose-escalating, randomized multicenter trials. A total of 78 patients (40 Paricalcitol injection, 38 placebo) achieved treatment phase eligibility, which included intact parathyroid hormone (iPTH) > or = 400 pg/ml, normalized serum calcium levels between 8.0 and 10.0 mg/dl, and calcium x phosphorus product values less than 75. Study end points included a decrease in iPTH of at least 30% or a maximum of five dose escalations. After a 4-wk washout, paricalcitol or placebo was administered intravenously three times per week after dialysis for 12 wk. Study drug was started at a dose of 0.04 microg/kg and was increased by 0.04 microg/kg every 2 wk to a maximal allowable dose of 0.24 microg/kg or until at least a 30% decrease in serum iPTH was achieved. The dose of paricalcitol that decreased iPTH by at least 30% became the maintenance dose. Of 40 patients receiving paricalcitol, 27 (68%) had at least a 30% decrease in serum iPTH for 4 consecutive weeks, compared with three of 38 patients (8%) receiving placebo (P < 0.001). For patients who received 12 wk of treatment with paricalcitol, the levels of iPTH decreased significantly from 795+/-86 to 406+/-106 pg/ml (P < 0.001), whereas the values for PTH were 679+/-41 pg/ml before and 592+/-41 pg/ml after 12 wk of therapy in patients receiving placebo (P=NS). Also, there was a significant difference between treatment groups for the change from baseline PTH levels (P < 0.001). Paricalcitol treatment resulted in a significant reduction in serum alkaline phosphatase from 148+/-23 U/L to 101+/-14 U/L (P < 0.001) in patients treated for 12 wk compared with 120+/-9 U/L to 130+/-11 U/L (P=NS) in patients receiving placebo for 12 wk. Importantly, hypercalcemia did not occur before achieving target serum iPTH levels in any of the paricalcitol-treated patients. There was no significant difference for the change from baseline in serum phosphorus within or between treatment groups. There was no significant difference in adverse events between the paricalcitol and placebo-treated groups. These studies demonstrate that paricalcitol safely and effectively suppresses iPTH levels in hemodialysis patients. This second generation vitamin D analog may have a wider therapeutic window than current vitamin D preparations, and thus may allow reduction in PTH with less hypercalcemia.