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Alendronate sodium (121268-17-5)
Mechanism Of Action
Animal studies have indicated the following mode of action. At the
cellular level, alendronate shows preferential localization to sites of bone
resorption, specifically under osteoclasts. The osteoclasts adhere normally
to the bone surface but lack the ruffled border that is indicative of active
resorption. Alendronate does not interfere with osteoclast recruitment or
attachment, but it does inhibit osteoclast activity. Studies in mice on the
localization of radioactive [3H]alendronate in bone showed about 10-fold
higher uptake on osteoclast surfaces than on osteoblast surfaces. Bones
examined 6 and 49 days after [3H]alendronate administration in rats and
mice, respectively, showed that normal bone was formed on top of the
alendronate, which was incorporated inside the matrix. While incorporated in
bone matrix, alendronate is not pharmacologically active. Thus, alendronate
must be continuously administered to suppress osteoclasts on newly formed
resorption surfaces. Histomorphometry in baboons and rats showed that
alendronate treatment reduces bone turnover (i.e., the number of sites at
which bone is remodeled). In addition, bone formation exceeds bone
resorption at these remodeling sites, leading to progressive gains in bone
mass.
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