Tecalcet (also known as KRN-568; NPS-R-568; R-568), is an oral calcium channel agonist potentially for the treatment of hyperparathyroidism. Calcimimetics, such as Tecalcet, are agonists and activate the calcium channel in a non-competitive fashion. Tecalcet does not compete directly with calcium that activates the receptor through binding in the extracellular domain of these receptors, but rather, calcimimetics such as Tecalcet, bind allosterically in the seven transmembranes to ‘sensitize’ the receptor to extracellular calcium. Tecalcet acts as an agonist of the calcium receptors of the parathyroid cells, causing a decrease in PTH release. Tecalcet also acts on the parafollicular cells (C-cells) of the thyroid gland, resulting in an increase in calcitonin release. These effects ultimately lead to a decrease in plasma calcium concentrations. Studies in rats have shown that oral administration of R-568 at doses ranging from 3 to 100 mg/kg caused a rapid (<30 minutes) decrease in plasma PTH concentrations and an increase in calcitonin concentrations, accompanied by a dose-dependent decrease in calcium concentrations. Tecalcet had been in phase II clinical trials by for the treatment of hyperparathyroidism, postmenopausal osteoporosis and rheumatic disorders in Japan and US. Development of Tecalcet has been discontinued.