Alendronic acid, sold under the brand name Fosamax among others, is a bisphosphonate medication used to treat osteoporosis and Paget's disease of bone.

[4] Common side effects (1 to 10% of patients) include constipation, abdominal pain, nausea, and acid reflux.

These prenylated GTPases are necessary for various cellular processes including osteoclast morphology, endosome trafficking, and apoptosis.

The absorbed drug rapidly partitions, with approximately 50% binding to the exposed bone surface; the remainder is excreted unchanged by the kidneys.

Unlike with 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.