Alendronate sodium (Fosamax) is a bisphosphonate that acts as a specific inhibitor of osteoclast-mediated boneresorption. Bisphosphonates are synthetic analogs of pyrophosphate that bind to the hydroxyapatite found in bone.Alendronate sodium is chemically described as (4-amino-1-hydroxybutylidene) bisphosphonic acid monosodium salttrihydrate.

The empirical formula of alendronate sodium is C4H12NNa07P2-3H20 and its formula weight is 325.12.