The chemical formula is C4H12NNaO7P2. Another name is 4-Amino-1-hydroxybutane-1,1-diylbis(phosphonic acid. Alendronate is classified as a bisphosphonate, or a diphosphonate, or as a aminobisphosphonate.
Bisphosphonates have the P–C–P chemical structure. In the body, the alendronate attaches to the edges of the bone. There is slows the resorption of minerals to the bloodstream. Now a second effect of alendronate on the body is to inhibit mineralization of bones. At extremes, slowing mineralization leads to a disease called osteomalacia, aka rickets. This is an area where alendronate does better than other bisphosphonates. A good osteoporosis drug inhibits resorption, but does not stop mineralization. The amount of alendronate you have to take to effectively retard resorption is about 1000 times what you would have to take to stop mineralization, while for the bisphosphonate drug etidronate, the effective dose for osteoporosis treatment carries a substantial risk of causing osteomalacia. Osteomalacia hardly ever happens on alendronate.
Its Chemical Abstract Service designation (CAS Number) is 41575-94-4. The broader category of osteoporosis drugs is antiresorptive drugs that slow the "resorption" of minerals out of the bone and into the bloodstream. Other antiresorptives include SERMs (selective estrogen-receptor modulators) and calcitonin.
Inside the bone, alendronate binds to the enzyme farnesyl pyrophosphate which is involved terpenoid formation. Osteoclast turnover is reduced and bone resoprtion is slowed.
Bisphosphonates are not well absorbed in the digestive system (one to five percent of an oral dose), and absorption is best when the drug is given on an empty stomach. Alendronate is usually taken only with water and that the patient is advised to wait at least 30 minutes before ingesting food or other medications. Approximately 80 percent of the absorbed alendronate is cleared by the kidney, the remaining 20 percent being taken up by bone. Relative bone uptake is increased in conditions of high bone turnover, with less of the drug being excreted by the kidneys.
The half-life in the bloodstream is about an hour. The half-life in the body as a whole, however, is so long as to be meaningless - possibly over 10 years. This is one way bisphosphonates are different from other drugs. They are not metabolized in the sense that they are chemically broken down in the body, and they do not exit the body quickly after they become part of the bone.