Bisphosphonates in oncology
Bisphosphonates are analogues of pyrophosphate with a carbon instead of oxygen atom (P-O-P). They attach to the bone crystals and are absorbed by osteoclasts, which breakdown bone. Within the osteoclast, bisphosphonates interfere in the normal function and induce apoptosis. In addition, they decrease the depth of resorption cavities, therefore it slows remodelling rate and decreases resorption at each site of bone turnover. Thus, by inhibiting bone resorption, bisphosphonates freeze the cycle of bone remodelling.
Ibandronic acid is a potent bisphosphonate drug used in the prevention of bone complications with breast cancer and bone metastases.
Zoledronic acid is used to prevent skeletal fractures in patients with cancers such as prostate cancer and after different cancer therapies. It can also be used to treat hypercalcemia of malignancy and can be helpful for treating pain from bone metastases.
Pamidronic acid and zoledronic acid are administered intravenously; ibandronate and clodronate are orally available.
Major side effects of the oral bisphosphonates include GI-complaints since these drugs require administration on an empty stomach. Intravenously administered bisphosphonates can give flu like symptoms after infusion. Both iv and oral administered drugs can induce osteonecrosis of the jaw and hypocalcemia.