Parathyroid Hormone - Protecting Your Bones: Osteoporosis

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Parathyroid hormone

A synthetic hormone is another treatment available for osteoporosis. In November 2002, the FDA approved teriparatide (Forteo), a synthetic version of parathyroid hormone (PTH), for the treatment — not prevention — of osteoporosis in both men and postmenopausal women.

PTH is produced naturally in the body. It works in several ways to increase the amount of calcium in circulation. It promotes calcium absorption in the intestines and slows its excretion by the kidneys. It can also stimulate both bone formation and bone loss. While too much PTH accelerates bone loss, low doses of PTH given intermittently can increase bone mass and strengthen bone.

Unlike other osteoporosis medications that slow the rate of bone loss, PTH actually helps build new bone. It does this by increasing the activity and number of bone-building osteoblasts. As a result, it can increase bone mass dramatically; it's the only treatment that can potentially reverse bone loss. Studies have found that 21 months of treatment with teriparatide increased bone mineral density at the spine by 9.7% and at the hip by 2.6%.

Effects of parathyroid hormone (PTH) on bone These scanning electron microscopy pictures show bone biopsies taken from a 64-year-old woman, before (A) and after (B) PTH treatment. Improvements can be seen in interior structure (microarchitecture) and outer (cortical) thickness. Reproduced from J Bone Miner Res 2001; 16: 1846–1853 with permission of the American Society for Bone and Mineral Research

One study found that teriparatide was more effective than alendronate in increasing bone mineral density and decreasing fractures in postmenopausal women with osteoporosis. Teriparatide appears to reduce vertebral fractures by 65%–70% and to reduce nonvertebral fractures by about 50%.

While there was speculation that combining teriparatide with a bisphosphonate may improve the effects of the drugs, a study published in 2003 in the New England Journal of Medicine found that this was not the case. In the study, 83 men were assigned to one of three groups: one that took teriparatide, one that took alendronate, and one that took both. The researchers found that the men who took only teriparatide had the greatest gains in bone mineral density at the spine and hip, compared with the men in the other two groups. Thus alendronate appears to dampen the benefits of PTH. But the researchers also found that the men on combination therapy had greater gains in spinal bone mineral density than those taking only alendronate. So this study found that PTH therapy alone seems to be most effective at increasing bone density, while combination therapy works better than alendronate alone.

Teriparatide is currently recommended for people who have osteoporosis and are at high risk for a fracture. This includes people who have already suffered a nontraumatic fracture of the spine, hip, or another major bone, as well as people with multiple risk factors for fractures (such as a family history of osteoporosis, poor calcium intake, and a T-score of less than -2.5 on a bone mineral density).

Teriparatide is only available as a once-a-day injection. Because this is a new therapy and no long-term studies are available, most experts recommend that treatment be limited to no more than two years. Some experts recommend using PTH alone for two years and then using a bisphosphonate to protect or augment any gains in bone mineral density.

Side effects can include nausea, dizziness, and leg cramps. In animal studies, some rats that were given PTH developed a form of bone cancer, but in human studies, no cases have appeared.

Last updated:	January 23, 2007