Watts NB et al. (2008) Fracture risk remains reduced one year after discontinuation of risedronate. Osteoporos Int 19: 365–372

Risedronate affects multiple factors that contribute to bone strength and, therefore, is commonly used to treat osteoporosis. The reduction in fracture risk observed with risedronate might only be partially explained by changes in BMD and bone turnover markers (BTM).

Watts et al. analyzed the changes in BMD and BTM and their effects on fracture risk after discontinuation of risedronate. They studied postmenopausal women with osteoporosis who had completed a 3-year, double-blind treatment period, during which they received either risedronate or placebo. At the end of this period women could choose to stay in the study for 1 year after treatment was discontinued. This extension year was completed by 599 women.

In the year following discontinuation of treatment, BMD at the lumbar spine, femur and trochanter decreased significantly in women who had previously received risedronate, although their BMD remained higher than that of women who formerly received placebo. In risedronate-treated women, urinary measurements of bone resorptive markers and serum bone-specific alkaline phosphatase had decreased significantly during the 3 years of treatment, but were not significantly different from those of placebo-treated women after 1 year off treatment. After the extension year, however, the relative risk of vertebral fracture in previously risedronate-treated women was still reduced by 46% compared with previously placebo-treated women.

The authors concluded that a reduced risk of new vertebral fractures persisted in the year following discontinuation of risedronate treatment, despite an apparent resolution of risedronate's effect on BMD and on BTM.