Navicular syndrome—while common—is difficult to treat and causes lameness issues that negatively impact a performance horse's ability to train and perform. Before the availability of clodronate, equine veterinarians had few options to help keep afflicted horses in work. 

In 2014, the U.S. Food and Drug Administration (FDA) Center for Veterinary Medicine (CVM), approved non-nitrogenous bisphosphonate OSPHOS® (clodronate) to be used in horses 4 years of age and older to control clinical signs associated with navicular syndrome. Since then, it has gained widespread acceptance as an effective, non-invasive treatment for horses with navicular. 

To address the conclusions of an earlier 12-participant roundtable on bisphosphonate therapy in equine practice, a panel of experts spoke at a Dechra-sponsored Sunrise Session at the 2019 American Association of Equine Practitioners (AAEP) Convention. Sharing the important takeaways of the roundtable with attendees were Robert Boswell, DVM, PA, and Billy Maupin, DVM. 

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What was the objective of the roundtable?

The objective of the roundtable was to collect opinions and experiences from equine experts on the use of bisphosphonates in horses. The topics covered during the roundtable were: clinical impact, case selection, short- and long-term clinical efficacy and safety considerations. 

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Clinical Impact

Overall, panelists and roundtable participants were confident in administering OSPHOS® as part of a comprehensive management system. They made the following comments about the ways they have seen the drug make a difference:

○ "This has been a game-changer in a lot of ways, both as a standalone therapy and as an adjunct therapy to how I manage my sport horse medicine[...]. I almost always use it together with other more traditional therapies if I have osteoarthritis, if I'm looking at a horse that's got OA of the neck, SI conditions, certainly hocks and anything in the coffin joints, navicular region or front feet. If I'm going to treat that with joint injections, I always treat that with the OSPHOS®[...].

"The other thing it has done is, in some cases, it's made a big difference in horses where I'm not really sure what exactly is going on, but I think it's bone- or joint-related, maybe. We might use OSPHOS® to try and make a difference in that horse.

"Or a horse, for example, that may be cushanoid or insulin-resistant and the owner doesn't want to go through the expense of a big, long regenerative therapy treatment schedule. We might do that as a standalone therapy, use OSPHOS®

○"It has dramatically increased the weapons with which I can attack some of my more common problems." —Robert Boswell, DVM, PA

○"OSPHOS® has been the best drug we've come in a long time to actually get horses back in the show pen. [...] It's just improved the quality of life and the comfort of the horses. A lot of the horses, when you can identify a radiographic lesion or get an MRI diagnosis of some lysis, they're just very responsive to it. 

"Probably for us, for any of the lytic diseases, it's been good." —Billy Maupin, DVM

○“I think [clodronate] gives us another tool in our toolbox to address some of these issues that have potentially been refractory to other treatment modalities. In my practice, it is just part of what I do […]. There will be shoeing changes, work changes, looking at footing. It’s sort of the holistic approach.” —Sarah le Jeune, DVM, DACVS, DACVSMR

○“[Clodronate has] really opened up a great conversation with our clients and the ability to have a conversation about what is best for your horse, how do we treat your horse, long-term management, and looking at the whole horse rather than, ‘Just give a drug’, or ‘Just do an injection.” —Richard Markell, DVM, MRCVS, MBA

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Case Selection

Key takeaways in determining which horses would be most responsive to OSPHOS® as a treatment:

○ Panelists mostly agreed that radiographic, MRI or scintigraphy evidence of proof of changes and inflammation is a strong predictor of treatment success

○ MRI radiography is a diagnostic modality that can be used in determining whether to proceed with OSPHOS® as a treatment for horses with navicular syndrome 

○ Medical imaging should be used in conjunction with a comprehensive clinical exam that may include hoof tests, a palmar digital nerve block, and lameness and pain assessments to determine if concurrent soft tissue injury is involved

Roundtable panelists had the following comments: 

○ Based upon MRI findings I believe that the most responsive bone changes, such as those associated with the navicular bone or the insertion on the distal phalanx, rather than soft tissue issues, are a good place for OSPHOS® to be used.—Myra Barrett, DVM, DACVR

○ I agree, I see a lot of significant improvement when OSPHOS® is used to treat bone changes: “I think up until this point there hasn’t been a really good solution that was reliable as far as helping with the presumptive pain part of the bone changes [sclerosis] we’re seeing.” —Josh Zacharias, DVM, DACVS, DACVSMR

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Clinical Efficacy

Key takeaways about the short-term outcomes, long-term outcomes, redosing, rehabilitation and multimodal approach included: 

Short-Term Outcomes

○ Obvious improvement is expected in the short term, within 14 days

○ The OSPHOS® Clinical Efficacy Study showed 74% clinical improvement (at least 1 lameness grade) at 56 days

○  Short-term improvement reinforces diagnosis as bone pain or bone condition as the primary cause of lameness

○ “So the improvement, if we talk about heel pain […], we’re looking for an increase or an improvement in their lameness grades. And for me it’s not unusual for those to improve at least 2 lameness grades. I mean, I kind of expect that.” —Chris Ray, DVM, DACVS

Long-Term Outcomes

○ The OSPHOS® Clinical Efficacy Study showed that at 6 months, 64% of horses maintained improvement

○ “[Bisphosphonates have] been a game-changer in navicular disease. I can now manage it much better than I could 10 or 15 years ago. It has also allowed me now […], to have some more effective tools in conjunction with the other tools I’m using. So that’s how it worked for me.” —Kent Allen, DVM

Re-Dosing

○ Practitioners are encouraged to use clinical findings to guide their decision to re-dose clodronate

○ The need to re-dose should be based on clinical and physical examination; there is not always a need to re-dose

○ For recurrent conditions, redosing of clodronate is expected and can be safely administered per the label

Rehabilitation

○ Case dependent, though rehabilitation protocol does not need to change with administration of OSPHOS®

○ With mildly sore horses, training and showing schedules do not need to be interrupted

○ Panelists shared a common goal of minimizing the amount of time during which the horse is stall rested. 

○ Drawing from human medicine, the panelists acknowledge the importance of exercise and movement as part of the rehabilitation process

Multimodal Approach

○ Panelists agreed that clodronate should be considered an adjunct to other therapies

○ Shoeing adjustment was identified as one of the most important treatment modalities for heel-sore horses in conjunction with OSPHOS® administration

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Safety Considerations

Key safety considerations included: 

○ Panelists commented they felt comfortable with the wide safety margin of OSPHOS® with label-use 

○ Panelists felt that the risk of colic following clodronate administration is not a concern

○ Safety studies, including a recent study that examined CTX-1 levels following clodronate administration, refute a common concern among practitioners about the risk of atypical fractures;

○ Any post-injection signs of discomfort observed by panelists was mild and transient

○ The safe use of OSPHOS® has not been evaluated in horses less than 4 years of age and in  

○ The safe use of OSPHOS® has not been evaluated in pregnant or lactating mares or mares intended for breeding.

○ 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® (clodronate injection).

○ Horses should be well-hydrated prior to and after the administration of OSPHOS® due to the potential for adverse renal events. Water intake and urine output should be monitored for 3-5 days post-treatment and any changes from baseline should elicit further evaluation

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