Use of calcimimetics in uremic patients with secondary hyperparathyroidism:: Review

Recognition of the role of the extracellular calcium sensing receptor (CaR) in mineral metabolism has greatly improved our understanding of calcium homeostasis. The activation of this receptor by small changes in extracellular ionized calcium ((ec)(Ca2+)) regulates PTH, calcitonin secretion, urinary calcium excretion, and ultimately, bone turnover. The cloning of this CaR and the discovery of mutations making the receptor less or more sensitive to calcium allowed a better understanding of several hereditary disorders characterized either by hyperparathyroidism or hypoparathyroidism. This CaR became an ideal target for the development of compounds, the calcimimetics, able to amplify the sensitivity of the CaR to (ec)(Ca2+) suppressing PTH levels with a resultant fall in blood Ca2+. The first clinical studies with first-generation calcimimetic agents have demonstrated their efficacy lowering plasma intact PTH concentration in uremic patients with secondary hyperparathyroidism. However, the low bioavailability of these first calcimimetics predicts a difficult clinical utilization. The second-generation calcimimetic AMG-073, with a better pharmacokinetic profile, appears to be effective and safe for the treatment of secondary hyperparathyroidism, producing suppression of PTH levels with a simultaneous reduction in serum phosphorus levels and the calcium X phosphorus product. The advantage of controlling PTH secretion without the complications related to hypercalcemia, hyperphosphatemia, and increased calcium X phosphorus product is very promising.