Bone metabolism after cinacalcet administration in patients with secondary hyperparathyroidism

Cinacalcet, an allosteric modulator of a calcium (Ca)-sensing receptor, significantly suppresses parathyroid hormone (PTH) secretion and bone turnover rate in chronic hemodialysis (HD) patients with secondary hyperparathyroidism (SHPT). In this study, bone metabolism after cinacalcet treatment was examined, because hungry bone syndrome is sometimes experienced after parathyroidectomy in severe SHPT. We conducted a prospective observational study in 17 HD patients with SHPT. Cinacalcet was started at 25 mg/day, and the dose was increased step by step based on serum calcium level. A significant decrease in serum Ca and intact PTH concentration was found within 2 weeks. Tartrate-resistant acid phosphatase 5b, a good bone resorption marker, was significantly decreased at week 2 of the study. Serum bone alkaline phosphatase, a marker of bone formation, was increased at week 2 compared with the basal level. It became, however, gradually decreased until week 14. Only one patient whose bone turnover was considerably high had a mild numbness feeling. These results suggest that cinacalcet treatment might transiently accelerate bone formation with rapid suppression of bone resorption. This uncoupling could be involved in a mechanism by which cinacalcet decreases serum Ca level.