New insights into the role of teriparatide.

Parathyroid hormone (PTH) is secreted by the parathyroid glands and is an important regulator of blood calcium concentrations. Synthesis and secretion of PTH are stimulated by a decrease in blood calcium. PTH has three actions: 1) to increase the release of calcium from bone, 2) to reduce renal clearance of calcium, and 3) to stimulate the production of 1,25 (OH)2D3. Human parathyroid hormone is a single chain polypeptide with 84 amino acids and a molecular weight of 9425 Da. The N-terminal region, 1-34, is biologically active and sufficient for regulation of mineral ion homeostasis (1). Recombinant teriparatide {human PTH(1-34) [hPTH (1-34)]}, currently the only bone-forming osteoporosis drug available for clinical use, increases bone turnover with a greater stimulation of formation than resorption (2). Bone turnover markers also rise during treatment with teriparatide (TPTD), with markers of bone formation rising early and rapidly, followed by rises in bone resorption markers.