Relationship between Reductions in Parathyroid Hormone and Serum Phosphorus during the Management of Secondary Hyperparathyroidism with Calcimimetics in Hemodialysis Patients

Abstract

Background/Aim: The relationship between changes in plasma parathyroid hormone (PTH) and serum phosphorus levels during treatment with cinacalcet was evaluated in hemodialysis patients with secondary hyperparathyroidism (SHPT) receiving stable doses of vitamin D. Methods: Post hoc analysis of the relationship between PTH and phosphorus levels before and during treatment with cinacalcet in adult subjects on hemodialysis with inadequately controlled SHPT (PTH ≥300 pg/ml) included: (1) correlation of absolute changes from baseline in mean PTH and phosphorus at week 2 and during weeks 13–26; (2) phosphorus levels at baseline and absolute and percent change of phosphorus after cinacalcet administration stratified by baseline PTH level; (3) two regression analyses models were fitted that (a) adjusted for baseline lab values to quantify the relationship between changes in PTH and changes in phosphorus and (b) a multivariate regression analysis that adjusted for clinically relevant subject characteristics. Results: Serum phosphorus concentrations at baseline were incrementally greater by PTH stratum from lowest to highest. Reductions in PTH from baseline after 13–26 weeks of treatment with cinacalcet were associated with corresponding reductions in serum phosphorus. Two weeks after starting treatment with cinacalcet when doses of vitamin D analogues, phosphate binders, and cinacalcet remained unchanged, there was a statistically significant association (p < 0.0001) between the decreases from baseline in PTH and phosphorus. Conclusions: Reductions in PTH during cinacalcet therapy are associated with decreases in serum phosphorus that cannot be explained by changes in vitamin D or phosphate binder therapy, and may reflect diminished phosphorus release from bone.