The role of pamidronate in osteosarcoma patients
The first concern when dealing with osteosarcoma is the primary tumor and the potential discomfort that bone destruction from the tumor can cause (a process called lysis). Osteosarcoma is extremely painful for most dogs; it is very locally invasive and destructive to bone. In fact, this can ultimately weaken the bone enough to result in fractures created by minimal force (commonly referred to as a “pathologic fracture”). Amputation to remove the source of the pain (and the source of spread to other sites of the body) is ideal, but in cases that surgery does not appear to be amenable, we focus largely on pain management.
In people, bisphosphonates are helpful for pain relief, bone remineralization, as well as prolonged time to fracture of bone lesions, and in humans with metastatic bone tumors, similar drugs have actually shown to slow progression of the disease. Pamidronate is a bisphosphonate agent that can improve osteoclastic pain by binding to bone matrix and inhibiting the (tumor) cells that cause bone destruction thereby helping strengthen the existing bone, which can result in reducing the probability of pathologic fractures and decreasing bone pain.When studied in the laboratory, bisphosphonates have a direct toxic effect on bone cancer cells, contributing to their death, and there is also evidence that by inhibiting the growth of new blood vessels within the cancer, they also inhibit cancer growth.
In one paper, bisphosphonates were found to be effective to control pain in approximately 40% of dogs, with improved use of the leg for a median of 8 months – as compared to dogs with pain medications alone often experiencing a poor quality of life within 1-2 months of the development of lameness.
Pamidronate is given as an intravenous infusion over 2-3 hours. As pamidronate can adversely affect the kidneys in dogs, we decrease this toxicity by diluting the drug during administration. We also monitor urinalyses (creatinine and specific gravity values of significant value) and chemistries as we proceed with therapy. Improved comfort is seen in responders within 1-2 weeks of administration. Pamidronate can also be safely combined with other methods of pain relief (such as radiation therapy, NSAIDs or narcotics) for more effective pain control.
It generally is well tolerated with mild decrease in renal function being the most common side effect. Gastrointestinal side effects (e.g. nausea, vomiting, diarrhea or inappetance) may also occur but are usually transient and mild. If therapy is continued – typically at 3-4 week intervals so long as a response is seen - repeat thoracic radiographs are recommended periodically.
Prior to beginning treatment, radiographs of the limb are sometimes utilized to screen for any pathologic fractures. Thoracic radiographs to screen for metastasis are also frequently recommended. This process can be aided by sedation in an effort to decrease your pet’s pain during positioning.
If you are a veterinarian and have a patient that you think will benefit from this treatment, please call our office to request a phone consultation. You will need to submit a Phone Consult Request Form along with all the relevant patient information.
If your pet has been diagnosed with osteosarcoma and amputation is not an option, please call our office to schedule an initial consultation. In most cases, a referral from your pet's primary veterinarian is required.