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  • Writer's pictureSonoma Equine

Is it time to remodel..your horse's bones? Bisphosphonates can help.

Have you ever heard of the medications Tildren or Osphos? They are both in the drug class bisphosphonates. These are drugs that were traditionally used to treat osteoporosis (bone fragility) in humans. This is because bisphosphonates travel from the blood to the mineral matrix of bones, preferring to bind most at sites of active bone remodeling.

Bone remodeling is achieved by a balance of two processes: bone resorption (breakdown) by cells called osteoClasts, and ossification (new bone formation) by osteoBlasts. Bisphosphonate drugs are released from the mineral matrix by osteoClast activity (bone resorption) and enter osteoClasts, encouraging apoptosis (death) of these cells, and stopping bone resorption (see picture below). This allows osteoBlasts to move in and repair the "holes" left by the dead osteoclasts.

This action is why bisphosphonates are useful for treating lameness caused by navicular disease and bone "cysts" in other joints. Navicular and other bones with fluid-filled "cysts" are weaker than regular bone, and also do not allow for normal, smooth joint motion, which causes the horse pain. Stopping these cysts from increasing in size (which is controlled by osteoClasts) by treatment with bisphosphonates can greatly improve a horse's comfort. The effect is expected to last for 3-6 months or more. While these drugs may help many horses, they should be used with caution. Side effects can include potentially fatal damage to the kidneys (especially if given together with anti-inflammatory medications such as Bute/Banamine/Equioxx or the horse becomes dehydrated), and colic-like signs due to muscle cramping when the drug is initially traveling from the bloodstream to the bones.

Be sure to ask your veterinarian if a bisphosphonate might be the right treatment choice for your horse.

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