Differential effects of paricalcitol and calcitriol on intestinal calcium absorption in hemodialysis patients

Background/Aims: Increased parathyroid activity associated with chronic kidney disease is often managed with calcitriol, which can elevate serum calcium (Ca) by increasing bone resorption and intestinal absorption, whereas paricalcitol promotes less bone resorption. This study compared intestinal Ca absorption in hemodialysis patients treated with calcitriol versus paricalcitol (dose ratio 1:3). Methods: Patients (n = 22) aged ≥20 years, on maintenance hemodialysis for ≥2 months with intact parathyroid hormone (iPTH) levels of >200 pg/ml were enrolled in a single-center, double-blind, active-controlled, randomized, crossover trial. Mean fractional intestinal Ca absorption (±SE) was measured by the single-tracer method ( ⁴²Ca) and evaluated with an analysis of variance crossover model. Results: Mean fractional intestinal Ca absorption was significantly lower after paricalcitol (0.135 ± 0.006) versus calcitriol treatment (0.158 ± 0.006, p = 0.022), a 0.023 difference in absolute Ca absorption fraction. Overall Ca absorption was low in the study population, indicating that regulation of Ca absorption may be dysfunctional. There were no significant differences in serum PTH, Ca, phosphorus (P), or Ca × P. Conclusion: Overall, paricalcitol-treated patients absorbed ∼14% less Ca compared with calcitriol-treated patients with similar effects on PTH. In hemodialysis patients, paricalcitol may provide a benefit by lowering the Ca available for removal by dialysis and/or for deposit in bone or soft tissues.