Do bisphosphonates keep working after women stop taking them?

Women who stop taking alendronate after 5 years do not seem to be at any greater risk for fractures than women who continue treatment, but they do seem to experience a moderate decline in bone mineral density (BMD) and a gradual rise in chemical markers associated with fractures.

The findings come from The Fracture Intervention Trial Long-term Extension (FLEX), a study of just over 1,000 postmenopausal women randomized to receive 5 mg/d or 10 mg/d alendronate or placebo for 5 years.

Compared to women who continued taking alendronate past the 5-year mark, those who quit had less BMD at the total hip (–2.4%) and spine (–3.7%), but mean levels remained at or above pretreatment levels from 10 years prior. The women who quit treatment also had 55.6% (P<0.001) higher levels of C-telopeptide of type 1 collagen, 59.5% (P<0.001) higher levels of serum N=propeptide of type 1 collagen, and 28.1% (P<0.001) higher levels of bone-specific alkaline phosphatase, but after 5 years without therapy, levels remained somewhat below pretreatment levels of 10 years earlier.

Black DM, Schwartz AV, Ensrud KE, et al. Effects of continuing or stopping alendronate after 5 years of treatment. The Fracture Intervention Trial Long-term Extension (FLEX): a randomized trial. JAMA. 2006;296:2927-2938.