The study is the longest test yet of Fosamax, which was approved in 1995. It has gained quickly in popularity as an alternative to hormone supplements, which have been linked in recent years to heart disease and cancer.
The chronic condition requires long-term treatment, so that is good news, said Dr. Henry Bone, the study's lead author at St. John Medical Center in Detroit and director of the Michigan Bone & Mineral Clinic.
"The effects of the drug on the bone cells and the effect on the amount of bone were sustained over a full ten years," he told CBS Radio News. "The results have been very solid and consistently reproducible from one study to another."
The study was published Thursday in The New England Journal of Medicine. The group had reported previously on the first several years of findings in the 10-year experiment. Reporting on the last five years, the international researchers focused on 247 middle-aged and elderly women with postmenopausal osteoporosis.
The findings are likely to reassure doctors as well as patients who take Fosamax, known generically as alendronate.
About 8 million American women and 2 million men have osteoporosis. About 34 million others are at elevated risk. The disease is blamed for about 1.5 million broken bones a year, including many debilitating fractures of the hip and back.
The blockbuster drug, which raked in $2.7 billion in world sales last year, works by readjusting the continuous process of bone renewal. It slows bone-destroying cells and thus gives more time for bone-building cells to catch up. Doctors have wondered, though, whether the slower turnover might eventually do harm. Will bone finally begin to break as older, more calcified tissue becomes more predominant?
In this study, that did not appear to happen.
The number of fractures in the final five years was too small to be considered statistical proof. However, the raw numbers were seen as encouraging. Among women who took 10 milligrams of Fosamax daily, 5 percent suffered back fractures. Among women who stopped taking the drug during the last five years of testing, 6.6 percent had such breaks.
"The name of the game in osteoporosis treatment is fracture protection. That's why this study is so interesting," said Dr. Steven Harris, a bone specialist at the University of California at San Francisco.
Bone density measurements were also heartening. The 10-milligram group gained almost 14 percent in bone density in the lower spines over a decade, including nearly 4 percent over the last five years. The group that stopped taking the drug boosted its bone density in the lower back by 9 percent over 10 years — but nearly all of that took place during the first five years.
In the first group, hip bone also became denser, by almost 1 percent, over the last five years. The comparison group lost almost 2 percent.
The research was backed by the maker of Fosamax, Merck & Co. of Whitehouse Station, N.J. Several researchers disclosed ties to Merck.
Dr. Gordon Strewler, a bone specialist at Harvard Medical School, said this study does not fully resolve the question of whether Fosamax will eventually weaken bones, as it did at high doses in some animal tests. He now plans to reevaluate his own patients after 10 years. He predicted that some will take a lower dose, others will suspend use, and some will stop altogether.
Osteoporosis chiefly strikes women after menopause, Almost one in two women over 50 is expected to break a bone as a result of osteoporosis.