SNOWMASS, COLO. — The current evidence suggests it is a very small group of individuals with low bone density who should be treated with parathyroid hormone, Dr. Lenore Buckley said at a symposium sponsored by the American College of Rheumatology.
Probably the only patients who are proper candidates for parathyroid hormone (PTH) therapy, according to a recent cost-effectiveness analysis, are those patients who have an extremely low T score, below −3.5, and who are at least 70 years old or have had a vertebral fracture, said Dr. Buckley, a professor of internal medicine at Virginia Commonwealth University, Richmond.
The cost-effectiveness analysis to which she referred considered the case of a postmenopausal woman with osteoporosis and compared four different treatment strategies: calcium and vitamin D supplementation, 5 years of treatment with alendronate, 2 years of PTH therapy, and 2 years of PTH followed by 5 years of alendronate.
The analysis said that vitamin D supplementation and the alendronate treatment fell within the cost range that is considered economical. The 5 years of alendronate treatment cost $15,800 per quality-adjusted life year gained. The 2 years of PTH therapy alone was not as effective as the alendronate alone regimen, and cost more. And the combined PTH followed by alendronate regimen cost $157,500 per quality-adjusted life year gained, which is considered well outside the range of cost effectiveness.
It was only when the risk of fracture became very high that the combined regimen began to become cost effective.
Those findings appear to be practical and to reflect what recent research indicates about PTH treatment, Dr. Buckley said.
PTH does seem to produce greater increases in bone density than bisphosphonates, and in patients who are at high risk of fracture, the hormone appears to reduce the rate of fracture by approximately 65% over 2 years, she said. But PTH also costs about $7,000 a year, and patients have a hard time with the required daily injections.
A number of recent studies have looked at combining PTH with bisphosphonates as a way to either improve on the density gains or make treatment easier.
Those studies have found that it is possible to get some additional benefit when PTH is used cyclically (3-month cycles) with continuous bisphosphonate treatment and that there may be some benefit in using PTH in patients who do not seem to be responding to bisphosphonate treatment.
But, in general, combining the two appears to dampen the gains in density that are achieved with PTH alone, probably because it is not possible to fully uncouple bone resorption, which is prevented with bisphosphonate treatment, from bone formation, which is stimulated by PTH, Dr. Buckley said.
She said that given the length of activity of bisphosphonates, it probably would take a patient about 1 year off bisphosphonate treatment to be ready to reap the full benefit of PTH.
However, the present evidence suggests it's possible to consolidate gains achieved with PTH treatment by following it with a bisphosphonate; a year of PTH followed by a year of alendronate can produce a 12% increase in bone mineral density in the lumbar spine.