Bone disease in uremic patients: advances in PTH suppression

Chronic renal failure is often complicated by altered calcium and phosphate omeostasis. Many patients develop secondary hyperparathyroidism during the course of the disease. Therefore, both prevention and treatment of secondary hyperparathyroidism are central issues in the treatment of uremic patients. Active vitamin D metabolites are important agents in uremic patients, who have a defective activity of the renal 1alpha-hydroxylase responsible for calcitriol synthesis. Howewer, treatment with calcitriol has some limitations, namely an increase in intestinal phosphate absorption, a possible calcium overload and therefore an increase in CaxP ion product. These limitations stimulated an active research on the development of vitamin D analogs with reduced effects on intestinal transport as well as on bone mobilization of calcium and phosphate. Three vitamin D analogs, which have been used in humans, are reviewed in this article: 22-oxacalcitriol (Maxacalcitol), 19-nor-1alpha,25(OH)2 vitamin D2 (Paricalcitol), and 1alpha(OH) Vitamin D2 (Doxercalciferol). In addition, a new pharmacologic approach to the treatment of secondary hyperparathyroidism has been developed: the use of agonists for the parathyroid calcium sensing receptor, or calcimimetics. AMG O73, a second generation agent, is now under clinical evaluation in phase 3 studies, and it will soon be available in clinical practice. Given the different mechanism of action, it will be possible to use it along with vitamin D analogs and non calcemic phosphate binders. A broader spectrum of therapeutic approaches will enable the nephrologist to individually tailor the treatment of secondary hyperparathyroidism.