Dog Cancer Pamidronate (Aredia)

Background

When we think of our skeletons we commonly imagine a structure made of white bones that serves as a supportive structure to our softer tissues. It is easy to forget that living bone is an active tissue that grows, remodels, heals, and requires blood flow. Its marrow (pulpy portion in it) serves as the source of our blood cells. The bone stores and releases calcium and phosphorus that our soft tissues need for proper muscle contraction and metabolism. As we exercise and create greater demand on our muscles, our bones must change as well to strengthen and offer greater support.

New bone is constantly being laid down by cells called osteophytes and old bone is constantly being removed and reshaped by cells called osteoclasts. In the course of removing bone, the osteoclasts free up calcium for the circulation and are part of the complex hormonal system we use to regulate our blood calcium. The bisphosphonates are a class of medications that inhibit the osteoclasts, causing them to be less enthusiastic in their bone removal process or even killing them. There are several situations where it might be a good idea to interfere with the removal of old bone:

Bone Tumors
In this situation, a cancerous process destroys bone, a painful progression that promotes abnormal fracture. Bisphosphonates can be used to reduce bone destruction by the tumor, which is helpful in managing the pain as well as in strengthening the damaged bone. The most common bone tumor is the osteosarcoma.

Hypercalcemia of Malignancy
Some tumors secrete a protein called PTHrp, which stands for parathyroid hormone-related protein. This protein is misinterpreted by the body as parathyroid hormone, which serves to raise blood calcium. Too much circulating calcium causes the kidneys to fail, weakens bones, promotes mineralization of soft tissues, and other metabolic problems.

Bisphosphonates can be used to make the osteoclasts less responsive to this artificial hormone. Tumors most likely to create hypercalcemia of malignancy are: canine lymphoma, canine mammary tumors, parathyroid tumors, anal sac adenocarcinoma, or multiple myeloma. Read more about hypercalcemia.

Vitamin D Toxicity
Vitamin D toxicity is not something you normally have to worry about when taking supplements, though potentially it could come up if prescription active vitamin D (which is actually a hormone) is given medically. The most likely situation where vitamin D toxicity might come into play is when vitamin D analog rat and mouse poisons are used.

Research on bisphosphonates is on-going. There is some thought that they kill tumor cells directly and inhibit tumor spread. Pamidronate is one of the most commonly used bisphosphonates in veterinary medicine.

How this Medication Is Used

This medication is given as an intravenous infusion, meaning it is mixed into a large volume of fluid and given over several hours through a vein. When used to help bone tumor pain, infusions are given every 3 to 6 weeks.

Side Effects

Pamidronate has the potential to cause damage to the kidneys, which is why it is given as an infusion in a large volume of fluids. At least two hours of infusion seems to be enough to prevent kidney problems but periodic monitoring of kidney-related lab tests is a good idea if this medication is to be used repeatedly.

In humans, bone marrow problems have been reported in conjunction with pamidronate use (reduction in red blood cells, platelets or increased granulocytes).

Electrolyte imbalances may occur with pamidronate use.

Lab tests relevant to all the above issues are easily monitored. You may wish to discuss a regular testing protocol with your veterinarian if regular pamidronate infusions are planned.

Pamidronate overdose could manifest with a low blood calcium level. Twitching, anxiety, muscle weakness or seizures could result.

Interactions with Other Medications

Monitoring tests become extra important when pamidronate is used with medications that influence blood calcium levels or with drugs for which kidney toxicity is a concern. Other drugs that might be used in the same situations as pamidronate include:

Concerns and Cautions

Pamidronate may be a problem for patients with kidney insufficiency. Kidney function should be monitored if bisphosphonates are regularly used (see above).

Pamidronate should not be used in pregnant or nursing patients.

It is our policy not to give dosing information over the Internet.

 

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