Cinacalcet HCl: A Novel Treatment for Secondary Hyperparathyroidism Caused by Chronic Kidney Disease

Secondary hyperparathyroidism (SHPT) develops as a result of impaired calcium homeostasis when the failing kidneys disturb the complicated interactions between parathyroid hormone (PTH), calcium, phosphorus, and vitamin D. Twelve years ago, the calcium-sensing receptor (CaR) of the parathyroid gland was first cloned and identified as the principal regulator of PTH secretion. The activation of the CaR by small changes in extracellular calcium (_ec(Ca²⁺)) regulates PTH, calcitonin secretion, urinary calcium excretion, and ultimately, bone turnover. The CaR became an ideal target for the development of calcimimetics, which are able to amplify its sensitivity to _ec(Ca²⁺) suppressing PTH secretion. Cinacalcet HCl, a first-in-class calcimimetic, approved in both the United States and the European Union, offers a new therapeutic approach to the treatment of SHPT. The efficacy of cinacalcet HCl in treating SHPT in dialysis patients (n = 1,136) was studied in three similarly designed phase III clinical trials comparing patients receiving standard SHPT therapy plus cinacalcet HCl or plus placebo. Cinacalcet HCl, dosed from 30 to 180 mg/day, significantly reduced PTH while simultaneously lowering calcium, phosphorus, and calcium–phosphorus product in each of the three studies. Respective to the National Kidney Foundation–Kidney Disease Outcomes and Quality Initiative (NKF-K/DOQI) recommended targets for bone and mineral metabolism, 41% of cinacalcet HCl-treated patients achieved both PTH and calcium–phosphorus product targets, compared with only 6% in the placebo group. Results from 2 recent phase IIIb studies (TARGET and CONTROL) conducted in the United States also showed that cinacalcet HCl can significantly reduce or maintain reduction in PTH while simultaneously lowering calcium, phosphorus, and calcium–phosphorus product. In addition, patients taking vitamin D at baseline of these 2 trials were able to see significant mean reductions in vitamin D dose. Further assessment of cinacalcet HCl trial data has shown some important effects in SHPT patient clinical outcomes. A combined post-hoc analysis of clinical events using data from 4 (n = 1,184) cinacalcet HCl phase II and III studies suggests that treatment with cinacalcet HCl has a beneficial effect on relative risks of parathyroidectomy, fracture, and hospitalization for cardiovascular complications. Nausea and vomiting occurred more often in patients taking cinacalcet HCl than in those taking a placebo. There were also transient episodes of hypocalcemia in 5% of cinacalcet HCl patients versus 1% of placebo patients. However, these episodes were rarely associated with symptoms. The development of calcimimetics has already changed the treatment of SHPT in renal patients. Its effectiveness on the control of PTH secretion, along with simultaneous reductions in calcium, phosphorus, and calcium–phosphorus product, give this agent an advantage over traditional therapies in all levels of severity of SHPT.