FLEX (FIT Long-term EXtension) was a 5-year randomized, placebo (PBO)-controlled trial, designed to assess the efficacy and safety of long-term treatment with alendronate (ALN). 1099 postmenopausal women who had received 3-6 years treatment with ALN (5 mg/d during the first two years and 10 mg/d thereafter) in the Fracture Intervention Trial (FIT), were randomized to placebo (ALN/PBO) (N=437), ALN* 5 mg/d (N=329) or 10 mg/d (ALN/ALN) (N=333). Transilial bone biopsies were obtained following dual fluorochrome labeling from 31 women. Trabecular bone turnover, quantity, microarchitecture and mineralization were assessed. Twenty-nine specimens were suitable for quantitative back-scatter electron microscopy (qBEI; MCC and CAW), eighteen for histomorphometry (2D) and fourteen for micro-computed tomography (3D). Since there were no differences between the 5mg/d and 10mg/d ALN groups, the two groups were pooled. In this study, all patients were initially treated with ALN for ~5 years, followed by an additional five years of PBO or ALN. All patients in both ALN/PBO and ALN/ALN groups displayed double fluorochrome label in trabecular bone. The cortical and trabecular bone tissue of both groups appeared normal, lacking qualitative abnormalities such as woven bone, osteitis fibrosa, defective mineralization, and non-lamellar bone. There were no differences between the groups for any quantitative endpoint. These data, from a limited sampling, suggest that iliac trabecular bone tissue remains normal following use of ALN 5 or 10 mg/d for 5-10 years.
*Manufactured by Merck & Co., Inc, Whitehouse Station, NJ
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Faculty Member's Name: K.E. Ensrud, MD
Grants/Research Support: Merck
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