Management of secondary hyperparathyroidism has included the use of active vitamin
D or vitamin D analogs for the suppression of parathyroid hormone (PTH) secretion.
Although, these agents are effective, therapy is frequently limited by hypercalcemia,
hyperphosphatemia, and/or elevations in the calcium-phosphorus (Ca x P) product. In
clinical studies, paricalcitol was shown to be effective at reducing PTH concentrations
without causing significant hypercalcemia or hyperphosphatemia as compared to placebo.
A comparative study was undertaken in order to determine whether paricalcitol provides
a therapeutic advantage to calcitriol.
A double-blind, randomized, multicenter study comparing the safety and effectiveness
of intravenous paricalcitol and calcitriol in suppressing PTH concentrations in hemodialysis
patients was performed. A total of 263 randomized patients were enrolled at domestic
and international sites. Following the baseline period, patients with serum Ca x P
< 75, and a PTH level > or =300 pg/mL were randomly assigned to receive either paricalcitol
or calcitriol in a dose-escalating fashion for up to 32 weeks. Dose adjustments were
based on laboratory results for PTH, calcium, and Ca x P. The primary end point was
the greater than 50% reduction in baseline PTH. Secondary end points were the occurrence
of hypercalcemia and elevated Ca x P product.
Paricalcitol-treated patients achieved a > or =50% reduction from baseline PTH significantly
faster than did the calcitriol-treated patients (P = 0.025) and achieved a mean reduction
of PTH into a desired therapeutic range (100 to 300 pg/mL) at approximately week 18,
whereas the calcitriol-treated patients, as a group, were unable to achieve this range.
Moreover, paricalcitol-treated patients had significantly fewer sustained episodes
of hypercalcemia and/or increased Ca x P product than calcitriol patients (P = 0.008).
Paricalcitol treatment reduced PTH concentrations more rapidly with fewer sustained
episodes of hypercalcemia and increased Ca x P product than calcitriol therapy.