The Pharmaceutical Journal
Vol 275 No 7363 p218
20 August 2005

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Alendronate after PTH maintains bone density

Giving alendronate (Fosamax) to postmenopausal women after a year of parathyroid hormone therapy maintains bone mineral density, researchers have found. If parathyroid hormone (PTH) is not followed by treatment with an antiresorptive agent improvements in bone density are lost, they say.

The US researchers tested the effectiveness of the regimen in 119 post-menopausal women with low bone density. They observed a 31 per cent increase in spine bone density in the PTH-alendronate patients compared with a 14 per cent increase in those taking PTH followed by placebo for a year. During the second year, subjects given placebo lost substantial bone mineral density.

The study also looked at other regimens: taking alendronate alone for two years or taking PTH and alendronate for one year followed by a second year on alendronate. The PTH-alendronate treatment increased bone mineral density more than PTH-placebo in all bones studied and generally increased bone density more than the other two treatments, the researchers report (New England Journal of Medicine 2005;353:555).

The form of PTH used was PTH 1-84, which is related to teriparatide (Forsteo).

A second study in the same issue shows that PTH remains effective if it is given after a bisphosphonate but that its effect is blunted (ibid, p566). “While PTH following alendronate or in concurrent combination with alendronate may be less effective than PTH alone, our study clearly shows that alendronate following PTH provides an additive, perhaps synergistic effect,” Dennis Black, of the University of California, San Francisco, and lead investigator of the first study, concluded. “In this case one plus one may equal three or even four. Use of antiresorptive drugs following PTH seems to be the most effective way to combine these two classes of drugs.”