A drug used to treat certain bone conditions, such as osteoporosis and Paget disease of the bone. It is also being studied in the treatment of hypercalcemia (high levels of calcium in the blood) and bone pain caused by cancer. Fosamax slows the breakdown of bone and prevents the loss of calcium. It is a type of bisphosphonate.

The sodium salt of alendronate, a second generation bisphosphonate and synthetic analog of pyrophosphate with bone anti-resorption activity. Alendronate sodium binds to and inhibits the activity of geranyltranstransferase (farnesyl pyrophosphate synthetase), an enzyme involved in terpenoid biosynthesis. Inhibition of this enzyme prevents the biosynthesis of isoprenoid lipids (FPP and GGPP) that are donor substrates of farnesylation and geranylgeranylation during the post-translational modification of small GTPase signalling proteins, which is important in the process of osteoclast turnover. As a result, osteoclast activity is inhibited and bone resorption and turnover are reduced.