Endocrine Abstracts

Parathyroid hormone (PTH) is a novel treatment for osteoporosis, that stimulates bone formation and turnover, unlike current treatments that are antiresorptive in their actions. Both the entire molecule (1-84hPTH) and the amino-terminus of the molecule (1-34hPTH) are being studied in clinical trials. In 8 recent clinical trials (two involving males with osteoporosis) PTH has been shown to produce larger increments in vertebral bone mass than any currently available agent. In some, but not all of the studies, PTH also produces increased bone mass in the hip and in total body bone mass. The increases at non-vertebral sites are less than in the spine. In our original study we provided preliminary data suggesting that PTH could reduce the risk of vertebral fracture by 70%. A recent large clinical trial involving 1637 postmenopausal women with osteoporosis, median follow-up being 21 months, showed that PTH could increase bone mass and dramatically reduce the risk of both vertebral fracture (RR 0.35; CI 0.22, 0.55) and non-vertebral fractures (RR 0.46; CI 0.25, 0.88). In histomorphometric studies we see increased bone formation at sites of remodeling and also at previously inactive surfaces. Bone formation is also evident in cancellous bone and on both inner and outer aspects of cortical bone. Apposition of new bone on the periosteum, which would increase bone size, may be one way in which PTH produces marked effects on fractures.