Articles by Renee Tucker, DVM:
This article is about biphosphonates. These include Tildren and OsPhos.
For the purpose of easier reading, Osphos is equivalent to Tildren. Osphos is given IM and Tildren is given IV.
OsPhos works by stopping Osteoclasts. Here’s why this is bad.
The body has a lovely balancing system of osteoblast and osteoclast cells. These guys are in charge of making bone. The ‘clasts clear the way. They remove old bone cells. The ‘blasts build new bone cells.
The ‘blasts’ and ‘clasts work together. There cannot be any new bone cells laid down on the bone matrix unless the ‘clasts have cleared the way first. OsPhos stops this process.
Why do vets give OsPhos?
OsPhos is currently approved only for navicular disease. In navicular disease, the navicular bone appears to have less density. Less density on xrays means that it has less calcium. That is, less bone.
So vets think, “Ok, there’s less bone than we want. The problem must be too much osteoclast action! Let’s slow that down.” And they give OsPhos.
I don’t know if any veterinarian said, “Um, wait a minute. Couldn’t it also be too little osteoblast behavior? Or maybe the bone is under excessive strain and that’s why it’s losing calcium?”
Maybe someone did. But, nevertheless, Osphos and Tildren are still being given at time of this writing. And they’re given to horses for any perceived skeletal issue, not just navicular issues.
Side Effects with OsPhos
But the OsPhos goes to every bone, not just in the problem area. OsPhos is given IM (intramuscular). It can be found circulating in the bloodstream for four months. OsPhos releases from the bones — where it’s trapped — over months and years. During that time period, the bone balancing system is devastated. The majority of ‘clasts are out of commission. And therefore the ‘blasts can’t build bone.
It’s no wonder that fractures are listed on the side effects of OsPhos. Along with:
In addition, it’s worth noting that Tildren was discontinued for human use before it was made available for horses. When humans were given Tildren, chronic pain was a common reported side effect.
What to do instead of OsPhos:
If you or your vet is considering OsPhos/Tildren injection for your horse, please don’t do it. Instead, find the primary cause and fix that.
For example, if your horse has navicular disease, most commonly this is caused by contracted heels, misaligned leg, and poorly functioning stay apparatus. These can be corrected by TBT bodywork and knowledgeable trimming over time.
There’s always an answer. Just keep digging for the why.
Renee Tucker, DVM