Treating Osteoporosis with Parathyroid Hormone: When and How to Do It
Treating Osteoporosis with Parathyroid Hormone: When and How to Do It
Abstract & Commentary
By Joseph E. Scherger, MD, MPH Clinical Professor, University of California, San Diego Dr. Scherger reports no financial relationship to this field of study.
Synopsis: Two recent studies shed further light on the short-term use of parathyroid hormone (PTH) to enhance the treatment of osteoporosis. PTH is approved for use up to 2 years in patients with moderate-to-severe osteoporosis. The anabolic bone formation induced by PTH is largely lost after stopping therapy, but is well maintained by continued therapy with a biphosphonate. PTH may be given continuously or cyclically to enhance bone formation.
Sources: Black DM, et al. One year of alendronate after one year of parathyroid hormone (1-84) for osteoporosis. N Engl J Med. 2005;353:555-565; Cosman F, et al. Daily and cyclic parathyroid hormone in women receiving alendronate. N Engl J Med. 2005;353:566-575.
Parathyroid hormone (pth) is given by daily subcutaneous injection and is approved for up to 2 years in the treatment of moderate-to-severe osteoporosis. The reasons for the short-term use are twofold. First, the early studies of PTH in rats showed an increased risk of osteosarcoma with longer-term use, a finding which has been discounted by further analysis. More importantly, the benefits of PTH in causing bone formation appear to be short lived, mainly during the first 6-12 months of therapy, although some benefits have been shown for up to 2 years. The early increased bone formation with PTH before resorption has been called the anabolic window.
Previous research by Black and colleagues reported in 2003 showed that while PTH was highly effective in treating osteoporosis, concomitant therapy with a bisphosphonate offered little addition benefit.1 In addition, this earlier research showed that the benefits of short-term PTH administration were diminished after therapy was discontinued. In the new study referenced here, Black et al showed that the benefits of PTH therapy are largely maintained by administering a bisphosphonate continuously after PTH therapy.
Cosman et al studied a new use of this novel therapy for osteoporosis, by administering PTH in 3-month cycles for one year, comparing it with daily therapy with PTH, and comparing both regimens with a bisphosphonate. A control group took a bisphosphonate only. These researchers hypothesized that the enhanced anabolic effects seen with PTH in the first months of therapy might be repeated with the 3-month cycles. They found that PTH increased bone mineral density over bisphosphonate alone by 6.1% with daily PTH and 5.4% with cyclic PTH. While they did not find an enhanced benefit of the cyclic therapy, they confirmed the treatment value of PTH to increase bone mineral density.
It should be noted that the number of subjects in both of these studies was small, 119 in the Black et al study and 126 in the Cosman et al study. With these small numbers and the short term follow-up, no statement can be made to demonstrate that the PTH therapy prevented fractures.
Commentary
While osteoporosis continues to increase among both men and women, major strides have been made in its treatment. The same issue of the New England Journal of Medicine which reported these studies has an excellent clinical review of postmenopausal osteoporosis.2 Lifestyle and pharmacologic options are available for both prevention and treatment. Bisphosphonates have emerged as the preferred first-line agents for most postmenopausal women.
When patients have moderate-to-severe osteoporosis, the stakes are higher to protect bone and prevent fractures.For these high-risk patients, 1-2 years of therapy with PTH should be considered. As with the patients studied here, many of them have been taking a bisphosphonate and this should be continued while receiving the PTH although the additional benefit during combined therapy is small. There is no downside to combined therapy, and weekly or monthly use of a bisphosphonate is convenient. What is most exciting about these new data is that the benefits of administering PTH for 1-2 years are maintained when the bisphosphonate is continued. We may now with confidence give these high-risk patients a boost in bone mineral density which lasts. Admittedly, the data for fracture prevention with PTH are still lacking.
References
1. Black DM, et al. The effects of parathyroid hormone and alendronate alone or in combination in postmenopausal osteoporosis. N Engl J Med. 2003;349: 1207-1215.
2. Rosen CJ. Clinical practice. Postmenopausal osteoporosis. N Engl J Med. 2005;353:595-603.
Two recent studies shed further light on the short-term use of parathyroid hormone (PTH) to enhance the treatment of osteoporosis. PTH is approved for use up to 2 years in patients with moderate-to-severe osteoporosis. The anabolic bone formation induced by PTH is largely lost after stopping therapy, but is well maintained by continued therapy with a biphosphonate. PTH may be given continuously or cyclically to enhance bone formation.Subscribe Now for Access
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