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Bayhill Equine

Bisphosphonate Therapy

Bisphosphonates are a class of drug commonly prescribed to prevent bone loss in people. While OSPHOS is not used for this purpose in horses, knowing how Bisphosphonates work on people will help you better understand this class of drugs.

Brown horse receiving an injection from a Veterinarian


Bisphosphonates are a class of drug prescribed to prevent bone loss in people.

Bones undergo constant turnover with osteoblast forming bone and osteoclasts resorbing it. In normal bone tissue, there is a balance between bone formation and bone resorption. But in diseased bone tissue, this balance is disrupted.

Clodronate, the active ingredient in OSPHOS, is a bisphosphonate that in laboratory animal studies and in vitro studies is known to inhibit bone resorption by reducing number of active osteoclasts, regardless of the cause of osteoclast activity and it inhibits the formation and dissolution of calcium phosphate crystals in the bone matrix. Ultimately these actions lead to a decrease in the breakdown of bone.

While the exact mechanism of action of bisphosphonates in the horse is unknown this is the understood clinical pharmacology regarding clodronate at a cellular level and in other species.

Bone Remodeling

Navicular syndrome is known to cause stress and damage to the navicular bone leading to excessive bone remodeling. The normal bone remodeling pathway requires that bone resorption (digestion of bone) and new bone formation take place at the same site and in a coordinated fashion. Usually, the amount of bone formed during bone remodeling equals the amount destroyed. Any disruption in this balance results in disease to the bone, including bone loss.

During bone stress or disease, bone metabolism is accelerated and osteoclasts are stimulated to begin the remodeling cycle. Osteoblast follow behind the bone eating cells, but at a much slow pace. Accelerate bone resorption may exceed the bone rebuilding process during these times of chronic bone disease or stress.

What is OSPHOS?

OSPHOS is an injectable bisphosphonate indicated for the control clinical signs associated with Navicular syndrome in horses 4 years and older. OSPHOS is the only bisphosphonate approved by FDA for intramuscular use in horses. Your veterinarian will administer up to one vial of OSPHOS in 3 separate injection sites including neck, pectoral muscles and or gluteal muscles.

Owners are advised you observe their horse for at least two hours post-treatment for signs of colic, agitation, and/or nervous systems abnormalities. If a horse appears uncomfortable, nervous, or experiences cramping post-treatment the shown should be advised to contact their veterinarian and hand walk the horse for 15 minutes or until signs resolve.

*OSPHOS is a prescription drug product for use only by or the order of a licensed veterinarian.

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For more information about our ambulatory equine veterinary practice and the services we have to offer, please call our office at (650) 851-2300 or send us a message from our contact us page.