Opposite effects of calcitriol and paricalcitol on the parathyroid hormone-(1-84)/large carboxy-terminal-parathyroid hormone fragments ratio in patients with stage 5 chronic kidney disease

Background and objectives: The effects of calcitriol and paricalcitol on circulating levels of intact parathyroid hormone, parathyroid hormone-(1-84), the large carboxy-terminal-parathyroid hormone fragments, and the parathyroid hormone-(1-84)/ carboxy-terminal-parathyroid hormone fragments were studied. Design, setting, participants, & measurements: In the longitudinal study, 31 hemodialysis patients who were receiving intravenous calcitriol or paricalcitol were followed for 6 to 8 wk. After a washout period, patients were treated with the other vitamin D compound for 6 to 8 wk. Plasma intact parathyroid hormone and parathyroid hormone-(1-84) were measured, and the parathyroid hormone ratio was calculated. In the cross-sectional study, results of intact parathyroid hormone, parathyroid hormone-(1-84), and parathyroid hormone ratio were compared between patients who were treated with paricalcitol (n = 49) versus no vitamin D therapy (n = 44). Results: In the longitudinal study, the parathyroid hormone ratio was significantly lower in patients who were treated with calcitriol and higher with paricalcitol treatment compared with values that were obtained during washout. In the cross-sectional study, intact parathyroid hormone levels were identical in both groups, whereas parathyroid hormone-(1-84) and thus parathyroid hormone ratio values were higher in patients who were given paricalcitol than in patients who were not receiving vitamin D. Conclusions: These data show that at similar intact parathyroid hormone values, the active parathyroid hormone-(1-84) compound is lower with calcitriol than with paricalcitol treatment. This finding might be relevant for choice of vitamin D compound in patients with stage 5 chronic kidney disease.