Alendronic acid, sold under the brand name Fosamax among others, is a bisphosphonate medication used to treat osteoporosis and Pagets disease of bone. It is taken by mouth. Use is often recommended together with vitamin D, calcium supplementation, and lifestyle changes.Common side effects (1 to 10% of patients) include constipation, abdominal pain, nausea, and acid reflux. Use is not recommended during pregnancy or in those with poor kidney function. Alendronic acid works by decreasing the activity of cells that break down bone.Alendronic acid was first described in 1978 and approved for medical use in the United States in 1995. It is available as a generic medication. In 2019, it was the 96th most commonly prescribed medication in the United States, with more than 7 million prescriptions. Medical uses
Prevention and treatment of female osteoporosis
Treatment of male osteoporosis
Prevention and treatment of corticosteroid-associated osteoporosis together with supplements of calcium and vitamin D
Pagets disease

Contraindications
Alendronate should not be used in:

Acute inflammations of the gastrointestinal tract (esophagitis, gastritis, ulcerations)
Clinically manifested osteomalacia
Certain malformations and malfunctions of the esophagus (strictures, achalasia)
Inability to stand, walk, or sit for 30 minutes after oral administration
Renal impairment or chronic kidney disease as evidenced by a creatinine clearance below 30ml/min
Hypersensitivity to alendronate or another ingredient in the product
Hypocalcemia
Pregnancy and breastfeeding
Patients below 18 yrs. of age, as no clinical data exists for this population

Side effects
Gastrointestinal tract:
Ulceration and possible rupture of the esophagus; this may require hospitalization and intensive treatment. Gastric and duodenal ulceration may also occur.
At least half an hour should pass after intake of alendronate before eating dairy products or taking the supplement or drug. Highly active vitamin D analogues or fluorides: no data is available. Concomitant treatment should be avoided. The additional beneficial effect of HRT (hormone replacement therapy) with estrogens/progestins or raloxifene in postmenopausal women with osteoporosis remains to be elucidated, but no interactions have been seen. The combination is therefore possible, but controversial. Intravenous ranitidine increases the oral bioavailability of alendronate. No clinical consequences are known. The combination of NSAIDs and alendronate may increase the risk of gastric ulcers. Both these drugs have the potential to irritate the upper gastro-intestinal mucosa. Pharmacology
Mechanism of action
Alendronate inhibits osteoclast-mediated bone-resorption. Like all bisphosphonates, it is chemically related to inorganic pyrophosphate, the endogenous regulator of bone turnover. But while pyrophosphate inhibits both osteoclastic bone resorption and the mineralization of the bone newly formed by osteoblasts, alendronate specifically inhibits bone resorption without any effect on mineralization at pharmacologically achievable doses. Its inhibition of bone-resorption is dose-dependent and approximately 1,000 times stronger than the equimolar effect of the first bisphosphonate drug, etidronate. Under therapy, normal bone tissue develops, and alendronate is deposited in the bone-matrix in a pharmacologically inactive form. For optimal action, enough calcium and vitamin D are needed in the body in order to promote normal bone development. Hypocalcemia should, therefore, be corrected before starting therapy. Etidronate has the same disadvantage as pyrophosphate in inhibiting mineralization, but all of the potent N-containing bisphosphonates, including alendronate, risedronate, ibandronate, and zoledronate, do not.