OSPHOS® (clodronate injection) is a member of the bisphosphonate drug class. Bisphosphonates are a group of pharmacological agents that have existed since the 1960s and are employed worldwide for osteoporosis and bone abnormalities in human medicine and research. There are two generations of bisphosphonates, non-nitrogenous (non-nitrogen containing) and nitrogenous (nitrogen-containing). OSPHOS is a first-generation non-nitrogenous bisphosphonate. This is the least potent class of bisphosphonate. The nitrogenous bisphosphonates are not approved for use in horses and work on a more complex pathway with a myriad of side effects as observed and documented in human medical literature.

Bones undergo constant turnover, with osteoblasts 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. The main effect of a bisphosphonate is to decrease bone resorption and bring the balance of osteoclast and osteoblast activity back to normal by reducing the activity of the osteoclasts. OSPHOS® (clodronate injection) inhibits bone resorption by binding to bone mineral (inhibiting formation and dissolution), and by exerting direct cellular effects on osteoclasts.¹

Bisphosphonates are used to treat navicular syndrome in horses. OSPHOS® (clodronate injection) gained approval in April 2014 by the U.S. Food and Drug Administration (FDA) Center for Veterinary Medicine (CVM) as a non-nitrogenous bisphosphonate drug indicated for control of clinical signs associated with navicular syndrome in horses 4 years of age and older. OSPHOS is the only FDA-approved product containing clodronate indicated for the control of clinical signs of navicular syndrome in horses and is available exclusively through licensed veterinarians.² OSPHOS has gained wide acceptance in equine veterinary medicine to address navicular syndrome in an effective and non-invasive manner.

Equine navicular syndrome is one of the most common lameness issues in the adult horse. It is defined as chronic forelimb lameness associated with pain arising from the navicular bone and closely related structures including the collateral suspensory ligaments of the navicular bone, distal sesamoidean impar ligament, navicular bursa, and the deep digital flexor tendon.³ Chronic pain associated with navicular syndrome has been reported as causing one-third of all chronic forelimb lameness in horses.⁴ The syndrome affects horses of many breeds and activity groups, typically 4 to 15 years of age.^5,6 The exact cause of navicular syndrome is unknown; however biomechanical influences are thought to be involved, causing damage to the navicular bone which leads to increased bone remodeling and bone destruction.

The safe use of OSPHOS has not been evaluated in horses less than 4 years of age. OSPHOS has been approved for horses 4 years of age and older because navicular syndrome manifests at this age or older in the horse. The effect of bisphosphonates on the skeleton of growing horses has not been studied; however, bisphosphonates inhibit osteoclast activity which impacts bone turnover and may affect bone growth. Dechra does not promote or recommend the use of OSPHOS in horses less than 4 years of age.

Dechra firmly believes OSPHOS® (clodronate injection) is safe to use in horses when label directions are followed. We have a strong veterinary team who work collaboratively to ensure consistency, quality and ethical patient care is priority with regards to the use of OSPHOS. Dechra has undertaken significant educational efforts since the product launched to inform the profession on the indicated safe use of the product and have a very high compliance rate with on-label use of the product, particularly in English sport and western performance horses. For example, just since early 2017, the veterinary professional services team has conducted more than 280 educational presentations on OSPHOS. As an American Association of Equine Practitioners (AAEP) Educational Partner, we are committed to working with and for the industry to gain additional understanding of the drug and its use in an on-label manner.

OSPHOS may be re-administered at 3- to 6-month intervals based on FDA approval safety studies. The exact timing of the re-dosing is variable based upon each case. Dechra recommends re-dosing be determined by an attending veterinarian who can evaluate recurrence of clinical signs.

Dechra is the manufacturer of OSPHOS and promotes the use of this prescription drug per product label/SPC which states the drug is approved for horses 4 years of age and older for the control of clinical signs associated with navicular syndrome in horses. Additionally, as the manufacturer we cannot be held responsible to publish all withdrawal times and recommend that you refer to existing rules and regulations governing medication use and consult other jurisdictions and organizations for guidance.

Known Performance Withdrawal Times (not comprehensive and does not encompass racing organizations/jurisdictions): The International Federation for Equestrian Sports (FEI) has listed clodronate as a prohibited substance-controlled medication for competing horses, but has not published a specific detection time so far. FEI has published a detection time of 28 days for tiludronate, a bisphosphonate similar to clodronate.

The British Horseracing Authority (BHA) has announced a stand-down period for veterinary licensed bisphosphonates (tiludronate and clodronate) of 30 days. Also, according to BHA regulation, the two drugs are not allowed to be used in horses under the age of 3.5 years.

The Canadian Pari-Mutuel Agency (CPMA) has set an elimination guideline of 30 days for horses four years of age and older. Additionally, according to CPMA regulation, the use of clodronate or tiludronate in a two or three-year-old horse is prohibited and any confirmed presence will result in a positive test. Testing for these drugs by the CPMA began on August 1, 2018.

The safe use of OSPHOS has not been evaluated in pregnant or lactating mares or mares intended for breeding. Bisphosphonates have been shown to cause abnormal fetal development in laboratory animals. The uptake of bisphosphonates into fetal bone may be greater than into maternal bone, creating a possible risk of skeletal or other abnormalities in the fetus. Bisphosphonates may be excreted in milk and absorbed by nursing animals. Although stallions were included in our (Dechra) field efficacy study, effects of OSPHOS on fertility were not studied. Dechra does not promote or recommend the use of OSPHOS in pregnant or lactating mares or horses intended for breeding.

The majority of adverse events associated with the labeled use of OSPHOS have been mild and selflimiting. Clinical signs exhibited are usually mild and transient and have included symptoms of abdominal pain (colic), discomfort, and agitation.

Bisphosphonates can cause renal toxicity. Higher blood plasma levels may increase the risk of toxicity. Bisphosphonates are excreted by the kidneys, therefore conditions and or medications that impair renal function may increase the blood plasma level and lead to more adverse reactions. Dechra does not recommend the use of OSPHOS in horses with impaired renal function. For additional safety information, click here see full prescribing information.

NSAIDs should not be used concurrently with OSPHOS. Concurrent use of NSAIDs with OSPHOS may increase the risk of renal toxicity and acute renal failure. As the majority of adverse events associated with the labeled use of OSPHOS have been mild and self-limiting, Dechra does not consider it necessary nor recommends pre-medication with an NSAID. Furthermore, pre-emptive administration of an NSAID could delay renal clearance of OSPHOS and may potentiate negative renal effects. Dechra recommends that NSAID therapy be discontinued before and after dosing with OSPHOS.

Dechra recommends monitoring horses for 2 hours following the administration of OSPHOS. If a horse appears uncomfortable, nervous, or experiences cramping posttreatment Dechra advises to hand-walk the horse until signs resolve. Owners should be advised to contact their veterinarian if the horse displays abnormal clinical signs. To report an adverse reaction, or to obtain a copy of the SDS for OSPHOS contact Dechra Veterinary Products at (866) 933-2472 or support@dechra.com. For more information and complete product information, visit www.dechra-us.com or www.osphos.com.