The action of Alendronate on bone tissue is based partly on its affinity for hydroxyapatite, which is part of the mineral matrix of bone. Alendronate also targets farnesyl pyrophosphate (FPP) synthase. Nitrogen-containing bisphosphonates (such as pamidronate, alendronate, risedronate, ibandronate and zoledronate) appear to act as analogues of isoprenoid diphosphate lipids, thereby inhibiting FPP synthase, an enzyme in the mevalonate pathway. Inhibition of this enzyme in osteoclasts prevents the biosynthesis of isoprenoid lipids (FPP and GGPP) that are essential for the post-translational farnesylation and geranylgeranylation of small GTPase signalling proteins. This activity inhibits osteoclast activity and reduces bone resorption and turnover. In postmenopausal women, it reduces the elevated rate of bone turnover, leading to, on average, a net gain in bone mass.
Alendronate, a second-generation bisphosphonate is the first member of a group of drugs which strengthens bone. Alendronate is used to reduce hypercalcemia in tumor-induced bone disease, to treat corticosteroid-induced osteoporosis and Paget's disease, and to prevent osteoporosis in postmenopausal women.
There is no evidence that alendronate is metabolized in humans or animals.
Alendronate can damage the esophagus both by toxicity from the medication itself and by nonspecific irritation secondary to contact between the pill and the esophageal mucosa, similar to other cases of "pill esophagitis."