Calcimimetic agents and secondary hyperparathyroidism: rationale for use and results from clinical trials.

Calcimimetic agents are small organic molecules that act as allosteric activators of the calcium sensing receptor (CaSR). In parathyroid cells, they lower the threshold for receptor activation by extracellular calcium ions and diminish parathyroid hormone (PTH) secretion. Calcimimetic compounds thus represent a novel way of controlling excess PTH secretion in clinical disorders such as secondary hyperparathyroidism (SHPT) due to chronic renal failure. Clinical trials have documented that the calcimimetic agent cinacalcet hydrochloride effectively lowers plasma PTH levels without increasing serum calcium or phosphorus concentrations in adult hemodialysis patients with SHPT. Serum phosphorus levels and values for the calcium-phosphorus ion product in serum often decline as plasma PTH levels fall during treatment. Experimental evidence suggests that calcimimetic agents may also impede the development of parathyroid gland hyperplasia, an integral component of SHPT due to chronic renal failure. Calcimimetic agents have considerable potential, therefore, as part of new therapeutic strategies for SHPT.