BACKGROUND: A significant number of kidney transplant recipients have low BMD. We hypothesized that calcitriol administration over the first year post-transplantation would protect the cortical skeleton in recipients managed without corticosteroids by suppressing PTH and bone remodeling. METHODS: In this double-blind, placebo-controlled trial, 67 participants aged ≥18 years on corticosteroid-sparing immunosuppressive regimen were randomized to daily calcitriol 0.5 mcg or placebo for 12 months after transplantation. The primary endpoint was the percent change in cortical density at the radius and tibia from pre- to post-calcitriol treatment compared to placebo as measured by HR-pQCT. Areal BMD was measured by DXA. Cortical and trabecular volumetric BMD and microarchitecture and total estimated bone strength were measured by HR-pQCT. Blood samples for bone metabolic markers were obtained at baseline, one- and twelve-months. All primary analyses were intent to treat. Safety was assessed for hypercalcemia and progression of vascular calcifications. RESULTS: Thirty-two participants received calcitriol and 29 received placebo
27 and 27 participants completed the study, respectively. Most participants were male and Caucasian. Baseline Z-scores at all sites were within 0.5 SD of the general population. At 12-months post-transplantation, there were no between group differences in: areal BMD, volumetric BMD, microarchitecture or bone strength, or serum levels of bone markers. Participants with versus without bone loss had a blunted anabolic response over 12 months measured by serum bone markers. Hypercalcemia was higher in the calcitriol group compared to placebo (p<
.001). No changes in arterial calcification scores were observed. CONCLUSIONS: In this randomized placebo-controlled study of calcitriol administration in kidney transplant recipients on corticosteroid-sparing immunosuppression, calcitriol did not improve bone quality and strength but was associated with higher rates of hypercalcemia.