Bisphosphonates are a class of drugs that prevent the loss of bone density, used to treat osteoporosis and similar diseases. They are the most commonly prescribed drugs used to treat osteoporosis. They are called bisphosphonates because they have two phosphonate (PO(OH) 2) groups. They are thus also called diphosphonates (bis- or di- + phosphonate). [url:https://en.wikipedia.org/wiki/Bisphosphonate]