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Chapter category: Endocrine

Vitamin D Analogs for the Treatment of Secondary Hyperparathyroidism in Chronic Renal Failure

Chapter authors:
Alex J. Brown

Secondary hyperparathyroidism (2oHPT) is a common complication in patients with chronic renal failure. The pathogenesis of 2oHPT is attributed primarily to phosphate retention and low serum 1,25(OH)2D3. Replacement therapy with calcitriol [1,25-dihydroxyvitamin D3 or 1,25(OH)2D3] or its precursor alfacalcidol [1?(OH)D3] often produces hypercalcemia, especially when combined with calcium-based phosphate binders. In addition, these natural vitamin D compounds can aggravate the hyperphosphatemia in these patients. Furthermore a high Ca x P product has been correlated with the severity of vascular calcification leading to coronary artery disease, the most common cause of mortality in renal patients. Several vitamin D analogs have now been developed that retain the direct suppressive action of 1,25(OH)2D3 on the parathyroid glands but have less calcemic activity, thereby offering a safer and more effective means of controlling 2oHPT. 22-Oxa-1,25(OH)2D3 (22-oxacalcitriol or OCT), 19-nor-1,25(OH)2D2(19-norD2) and 1?(OH)D2 are currently available in Japan (OCT) and the United States (19-norD2 and 1?(OH)D2). The mechanisms by which these analogs exert their selective actions on the parathyroid glands are under investigation. The low calcemic activity of OCT has been attributed to its rapid clearance which prevents sustained effects on intestinal calcium absorption and bone resorption, but still allows a prolonged suppression of PTH gene expression. The selectivity of 19-norD2 and 1alpha(OH)D2 is achieved by other mechanisms. A clear understanding of how these compounds exert their selective actions on the parathyroid glands may allow the design of more effective analogs in the future.

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