CALCITONINS AND OSTEOPOROSIS

Calcitonin, a polypeptide hormone secreted by the parafollicular C cel ls of the thyroid gland, lowers serum calcium by decreasing bone resor ption and tubular calcium reabsorption. An analgesic action, possibly mediated via beta-endorphins, is also evident. Parenteral calcitonin h as been shown to stabilise and increase indices of cortical and trabec ular bone mass and total body calcium when administered to patients wi th established osteoporosis. The routine use of this route of administ ration has been limited by poor patient compliance and tolerability. A n intranasal preparation of calcitonin provided a more convenient mean s of administration. Several clinical trials have shown that intranasa l calcitonin is effective and well tolerated both in prevention of pos tmenopausal bone loss and in established osteoporosis. Calcitonin ther apy is particularly indicated for patients with high-turnover osteopor osis where results show a net gain of bone mineral in the axial skelet on and a slowing of bone loss in the appendicular bones. Due to recept or downregulation a resistance to the hormone may occur after 12-18 mo nths of continuous treatment. This resistance can be avoided and delay ed by the cyclical or discontinued administration of the hormone. Furt her research is needed to confirm longer-term efficacy and effects on fracture rate.