Comparison of parathormone lowering effects of paricalcitol and calcitriol in hemodialysis patients.

BACKGROUND: Parathyroid hormone (PTH) levels may fluctuate in patients undergoing hemodialysis because of changes in calcium, phosphorus, and vitamin D levels. For these patients, the "Kidney Disease: Improving Global Outcomes" clinical practice guidelines recommend PTH levels be maintained in the range of two to nine times of the upper normal limit. Maintaining this balance is critical to prevent renal osteodystrophy. When the severity of hyperparathyroidism exceeds the recommended limits, vitamin D receptor agonists may be used for lowering PTH levels. Paricalcitol, as a biologically active vitamin D analog, is a selective activator of vitamin D responsive pathways. Both calcitriol and paricalcitol can be used as PTH-lowering agents. There is conflicting data about their comparative effectiveness for controlling hyperparathyroidism in patients undergoing hemodialysis and a meta-analysis revealed no differences between the two. AIM: To give real world data comparing paricalcitol and calcitriol as PTH-lowering agents in patients undergoing hemodialysis. METHODS: Patients undergoing hemodialysis whose PTH levels exceeded nine times of the upper normal limit were enrolled in the study. Depending on patient preferences, they were either given calcitriol or paricalcitol. Intravenous calcitriol was given 2 μg at the end of each dialysis sessions, and intravenous paricalcitol was administered as 5 μg twice per week. Demographic data, calcium-phosphorus levels, change in PTH levels in 6 months, and ratios of 25% and 50% reductions in PTH levels were compared between the two groups. RESULTS: A total of 21 patients were enrolled in this comparative study, eight patients received paricalcitol and 13 were prescribed calcitriol. A 50% reduction in PTH levels could be achieved in five patients in the paricalcitol group (62.5%); only one patient in the calcitriol group achieved the same reduction (7.6%). The difference was statistically significant (P = 0.014). However, there was no difference in the ratio of patients who had a 25% reduction in PTH levels (87.5% vs 38.4%; P = 0.067). PTH levels could be maintained in the targeted range in 87.5% of the patients in the paricalcitol group and in 69.2% of the patients in the calcitriol group (P = 0.36). However, PTH could be better suppressed under paricalcitol. Clinically important hyperphosphatemia or hypercalcemia was not observed in either the paricalcitol or the calcitriol groups. CONCLUSION: Although the PTH lowering effect of paricalcitol is stronger than calcitriol, both may help maintain PTH levels in the targeted range. Paricalcitol may be preferred for patients who have very high levels of PTH because it seems to cause a faster decline. Calcitriol may be preferred for a slower and limited decline. Prospective further studies with larger samples may be needed for a better comparison.