Most postmenopausal women who took the osteoporosis drug alendronate for 5 years and then stopped did not have an increased risk for nonvertebral fractures in the next 5 years, suggesting the medication has a lasting effect, according to a study in the current issue of JAMA.

Osteoporosis, common among postmenopausal women, is characterized by increased bone turnover (when aging bone is broken down faster than it can be replaced), progressive loss of bone mass and increased fracture risk.

Bisphosphonates are the most commonly used medications for postmenopausal osteoporosis. Alendronate, a potent bisphosphonate, decreases bone turnover, increases bone mineral density (BMD), and decreases vertebral, nonspine, and hip fracture risk in women with osteoporosis.

Treatment for osteoporosis often continues indefinitely, but few studies have examined the effects of using bisphosphonates longer than 5 years or the effects of stopping treatment after 5 years. Some studies have suggested that stopping treatment after several years might result in continued effectiveness because of a residual effect of the drug, but the magnitude and duration of this remains uncertain.

The Fracture Intervention Trial (FIT), a randomized, blinded, placebo-controlled trial, examined the effect of daily alendronate on BMD and fracture risk in postmenopausal women with low BMD. Average follow-up during treatment was 3.8 years, with optional open-label treatment continuation after trial completion.

In the article, Dennis M. Black, Ph.D., of the University of California, San Francisco, and colleagues report data from the FIT Long-term Extension (FLEX), which was designed to evaluate the effects on BMD of either continuation of alendronate, 5 or 10 mg/d for a total of 10 years, or discontinuation after approximately 5 years.

The researchers found that compared with continuing alendronate, switching to placebo for 5 years resulted in declines in BMD at the total hip (-2.4 percent) and spine (-3.7 percent), but average levels remained at or above pretreatment levels 10 years earlier.

Similarly, those discontinuing alendronate had increased serum markers of bone turnover compared with continuing alendronate, but after 5 years without therapy, bone marker levels remained somewhat below pretreatment levels 10 years earlier.

After 5 years, the cumulative risk of nonvertebral fractures was not significantly different between those continuing (19 percent) and discontinuing (18.9 percent) alendronate. Among those who continued, there was a 55 percent lower risk of clinically recognized vertebral fractures.

" the BMD and bone marker changes suggest some residual effect from 5 years of alendronate treatment that is evident for at least 5 years after discontinuation," the authors write.

"We conclude that continuation of alendronate for 10 years maintains bone mass and reduces bone remodeling compared with discontinuation after 5 years. The results confirm the safety of alendronate for up to 10 years including no increased fracture risk with long-term alendronate use.

However, even among those who discontinued therapy after 5 years, BMD remained at or above baseline values 10 years earlier and bone turnover was still somewhat reduced. Discontinuation did not increase the risk of nonvertebral fractures or x-ray-detected vertebral fractures over the next 5 years, but the risk of clinically diagnosed vertebral fractures was significantly increased among those who discontinued.

"These results suggest that for many women, discontinuation of alendronate after 5 years for up to 5 more years does not significantly increase fracture risk, but women at high risk of clinical vertebral fractures, such as those with vertebral fracture or very low BMD, may benefit by continuing beyond 5 years," the researchers write.