Bisphosphonate Drugs

Bisphosphonates are a class of drugs used to treat a variety of bone dissolution disorders such as osteoporosis, Paget’s disease and bone loss due to bone cancer. The bisphosphonates inhibit bone resorption. The total U.S. bisphosphonate market size was estimated at over $4.6 Billion in 2007 with the largest share being taken by Merck’s Fosamax (alendronate).

While the need for treatment of osteoporosis and other bone disorders is expected to increase at a rate of approximately 5 – 7% over the next 10 years due to the aging of the population, the bisphosphonate sales figures are expected to decrease. The total sales of bisphosphonates are expected to lose an estimated 30% of the market by 2011, due to recent and future approval of generic substitutions and the emergence of Specific Estrogen Receptor Modulators (SERMs) and synthetic Parathyroid Hormone Analogs (PTH), two fairly new classes of drugs approved to treat osteoporosis.

Bisphosphonates act by inhibiting osteoclast mediated bone resorption. They bind to hydroxyapatite which makes up 70% of healthy bone tissue and preventing dissolution of calcium from the hydroxyapatite. This in turn causes a reduction of bone resorption which is the release of calcium from the bone into the tissues and bloodstream. Excessive bone resorption due to aging or induced by medical treatment is the cause of osteoporosis in both men and women and a contributor to increased risk of bone fracture. Bone resorption in cases of bone cancer and bone metastases is responsible for not only porous bones, but also the painful condition of hypercalcemia of malignancy. Bone resorption and inappropriate reformation in Paget’s disease can also be treatable by bisphosphonates.

Some bisphosphonates are oral pills; others are given intravenously every month to several months. These drugs include: alendronate (Fosamax); etidronate (Didronel); pamidronate (Aredia); risedronate (Actonel); tiludronate (Skelid); zoledronic acid (Zometa). This website has information about side effects.

The nitrogen-containing bisphosphonates - alendronate, zoledronic acid, risedronate, ibandronate, and pamidronate - are more potent inhibitors of bone resorption than the simple bisphosphonates - etidronate, clodronate, and tiludronate.