Bisphosphonates
BISPHOSPHONATES – Please discuss all information with your vet
In humans, bisphosphonates are used to treat osteoporosis and to help lower high calcium levels due to certain types of cancer. They are also used to stabilize bones that are at risk for fracture from metastatic cancer or from multiple myeloma. The most common bisphosphonates are oral alendronate (Fosamax®), oral risedronate (Actonel®) and intravenous pamidronate (Aredia®).
In dogs, bisphosphonates are used as adjuvant therapy for the management of osteosarcoma. They inhibit osteoclast cells which are responsible for bone breakdown. This inhibition gives the osteoblast cells (bone builders) a chance to work without interference, strengthening the existing bone and creating new bone. Increasing the strength of the existing bone helps to decrease the risk of fractures, and stronger bone is less painful.
When studied in the laboratory, bisphosphonates also have a direct toxic effect on bone cancer cells, contributing to their death. There is also evidence that by inhibiting the growth of new blood vessels within the cancer, they also inhibit cancer growth.
The most commonly used bisphosphonate in the treatment of bone cancer in dogs is the intravenous pamidronate. It is used often in conjunction with radiation therapy, given in several cycles every few weeks. Recent studies have also shown that the oral alendronate may have a similar role in the stabilization of cancerous bone, by increasing the formation of healthy bone and decreasing the risk of fracture. There can be significant improvement in pain when bisphosphonates are used. Ongoing research suggests that bisphosphonates may also have a role in the inhibition of metastatic bone cancer cells, by their direct toxic effect. The indication for their use after amputation and chemotherapy remains to be defined, but there is promising laboratory evidence to support this theory.
The major side effects of bisphosphonates include gastrointestinal toxicity (nausea, vomiting, diarrhea or change in appetite) and kidney toxicity. Urine tests and electrolyte and kidney blood tests should be checked prior to institution of therapy and periodically during treatment, particularly if other medications such as anti-inflammatories are being prescribed. Intravenous pamidronate is usually administered over several hours. When the oral alendronate is prescribed, it is usually administered in the morning as a single dose, followed by a small meal 30 minutes later.