Parathyroid Hormone - Current Status

PTH or its analogues, given by subcutaneous injection once daily, are anabolic agents that directly stimulate osteoblastic bone formation, resulting in substantial increases in trabecular bone density in women with postmenopausal osteoporosis. It promotes new bone formation, leading to increased BMD. Teriparatide (Rdna Origin) is a biological product containing a portion of human PTH. It acts as endogenous PTH, thus regulating calcium and phosphate metabolism in bone and kidney. It works primarily to stimulate new bone by increasing number and activity of osteoblasts (bone-forming cells). Its additional physiological actions include regulation of bone metabolism, renal tubular reabsorption of calcium and phosphate, and intestinal calcium absorption. When administered with calcium and vitamin D, it increases BMD and decreases risk of fractures in patients with osteoporosis. Although in primary hyperparathyroidism bone catabolism prevails on bone anabolism, PTH remains a potent stimulator of osteoblasts and its anabolic properties can be seen when it is given at a low dose and intermittently. Intermittent PTH can stimulate bone formation to a greater extent and earlier than bone resorption, thus creating the so called "anabolic window"(1). Teriparatide is reserved for treating women at high risk for fracture, including those with very low BMD (T-score worse than -3.0) with a previous vertebral fracture. PTH improves BMD and reduces the risk of new vertebral (65%) and nonvertebral (54%) fractures