Bisphosphonates (Tildren & Osphos): Time to talk about the Skeleton in the closet

A question regarding the use of one of the above mentioned drugs circulated in my Facebook feed recently. It sparked much interest, confusion and curiosity by different readers…prompting me to write this post.

Bisphosphonates are a class of drug which includes both tildronate and clodronate. They were approved by the U.S. Food and Drug Administration in 2014 for controlling clinical signs associated with navicular syndrome in horses 4 years of age and older.

Since that time, some veterinarians have used these products off-label to treat other equine bone issues including osteoarthritis, bucked shins, sesamoiditis and subchondral bone cysts. Bisphosphonates are thought to provide significant analgesic effects and may even help improve radiographic images of conditions such as sesamoiditis. Whilst providing pain relief can be beneficial in appropriate situations, masking pain and accelerating bone damage and loss is not.

Like so many things in life- it would be nice to just to focus on what is convenient to us, whilst being ignorant of, or disregarding the depths of the truth. Maybe a bit like taking out a high interest loan to pay off a credit card debt, without addressing your income and expense habits: yep, you’ve conveniently paid off the credit card debt (which was your initial concern and source of stress) but guess what? Now you’ve got the extra cost of the loan (and the interest) you still need to pay off. You’ve just gone and dug yourself a bigger hole, whilst conveniently skirting around the original problem…

With our current level of knowledge and understanding of the actions of bisphosphonates, we should seriously question their use. Normally in horses, bone turns over continually (remodels). Cells called osteoclasts break down old bone while osteoblasts create new. This ensures bones remain strong and healthy and allows them to adapt to changes in exercise level or mechanical stress placed upon them. This adaptation and strengthening is an important mechanism in protecting against stress-induced injuries. Increased bone fragility has been seen in animals given high doses or long-term doses of bisphosphonates, a likely result of the inability to repair micro- damage within bone.

Bisphosphonates inhibit osteoclasts to block excess bone resorption. But they’ve also been shown to be anti-angiogenic (preventing new blood vessel growth). New blood vessel growth is an essential component to repair the normal micro-damage that naturally occurs during training and racing. Remember, normal repair and recovery of this micro-damage actually makes bones stronger. Furthermore, curbing osteoclasts interrupts the remodelling process: the activity of osteoblasts and osteoclasts is a finely balanced process. Inhibiting the activity of osteoclasts interferes with the osteoblasts, therefore they don’t kick into gear to build new bone. The FDA even blatantly state this, outlining that bisphosphonates inhibit osteoclast activity and decrease bone turnover, thereby potentially affecting bone growth. Ultimately, this inhibition of bone remodelling could place racehorses and performance horses at risk of greater numbers of and more serious injuries.

The safe use of bisphosphonates has not been evaluated in breeding horses or pregnant or lactating mares. Studies in laboratory animals have demonstrated bisphosphonates to cause abnormal foetal development, likely due to drug induced alterations in maternal and foetal bone uptake. Then there’s the inconvenient factor that bisphosphonates have a very long half life (meaning they potentially stay in the horse’s system many years after cessation of treatment). Add to this the fact that metabolites of bisphosphonates may be excreted in milk and absorbed by nursing animals…Hardly a winning start to a foal’s life…

So what can we do? Firstly, we need to address why there is a ‘problem’ in the first place, why we ‘need’ to be ‘treating’ a horse with such medications… This requires honestly and critically reviewing training, feeding/nutrition, recovery, medication use and management practices. If a horse has excessive inflammation and/or soreness in an area, it is a sign that things aren’t right. Without identifying and addressing the underlying cause of bone inflammation and injury the problem persists. Add the non-discriminate use of drugs which WE KNOW have serious side effects and you’ve gone and thrown a band-aid on a bullet hole, turning a blind-eye to the festering, seeping, infected wound beneath the temporary cover, which will fly off at some stage.

Honestly, who thinks creating short-term ‘soundness’ in the horse is worth the expense of creating a ‘crippled’ animal in the long term? Surely, we are smarter than that? Surely our horses deserve better than that?

Share this article to your socials