 alendronic acid (inn) or alendronate sodium (usan) â sold as fosamax by merck â is a bisphosphonate drug used for osteoporosis and several other bone diseases. it is marketed alone as well as in combination with vitamin d (2,800 iu and 5600 iu, under the name fosamax+d). merck's u.s. patent on alendronate expired in 2008 and the drug is now available as a generic. ==pharmacokinetics== as with all potent bisphosphonates, the systemic bioavailability after oral dosing is low, averaging only 0.6â0.7% in women and in men under fasting conditions. intake together with meals and beverages other than water further reduces the bioavailability. the absorbed drug rapidly partitions, with approximately 50% binding to the exposed bone surface; the remainder is excreted unchanged by the kidneys. unlike most drugs, the strong negative charge on the two phosphonate moieties limits oral bioavailability, and, in turn, the exposure to tissues other than bone is very low. after absorption in the bone, alendronate has an estimated terminal elimination half-life of 10 years.{{cite journal | author = shinkai i, ohta y | title = new drugs--reports of new drugs recently approved by the fda. alendronate | journal = bioorg. med. chem. | volume = 4 | issue = 1 | pages = 3â4 |date=january 1996 | pmid = 8689235 | doi
Bisphosphonates Merck