Effect of combined vitamin D receptor activator and lanthanum carbonate on serum fibroblast growth factor 23 level in predialysis patients (CVD-LAF study): design and method

Background: Whether vitamin D receptor activator (VDRA) use is beneficial in chronic kidney disease (CKD) is unclear, because it is possible that VDRA increases serum fibroblast growth factor 23 (FGF23) levels. We will conduct a randomized controlled trial in predialysis patients to determine the effect of VDRA alone or in combination with lanthanum carbonate (LC) on serum FGF23 levels. Methods: This is a single-center, open-label, randomized controlled trial. Enrollment will commence February 1, 2018, using the following inclusion criteria: (1) age ≥ 20 years, (2) CKD with an estimated glomerular filtration rate of 10–45 mL/min/1.73 m ² , (3) serum adjusted calcium level < 9.5 mg/dL, (4) serum phosphate level 4.0–6.0 mg/dL, and (5) serum intact parathyroid hormone (PTH) level ≥ 60 pg/mL. Study patients will be randomized 1:1 to receive alfacalcidol alone or in combination with LC. The initial dose of alfacalcidol will be 0.25–0.5 µg once a day according to serum adjusted calcium level. The initial dose of LC will be 250 mg once a day. We will measure serum intact and C-terminal FGF23 at 0, 4, 8, 12, 24, and 52 weeks. The primary outcome will be serum FGF23 level at 24 weeks compared with baseline. Discussion: This study aims to determine whether low-dose oral VDRA increases serum FGF23 level and whether the combination of VDRA and LC inhibits this increase. The results will be useful in the management of CKD–mineral and bone disorder in predialysis patients. Trial registration: UMIN000030503. Registered 20 January 2018.