Osphos and Tildren (Bisphosphonates)

These information sheets are provided for your interest. They should not replace veterinary advice from your veterinary surgeon.

Whilst every effort is taken to ensure the accuracy and completeness of the information provided, your specific circumstances must be discussed before advice can be given.

Fri, 20/05/2022 - 12:17 -- Ashley Stewart MRCVS

Bisphosphonates are drugs used to prevent or slow down bone damage and have been used for many years in human medicine as a primary treatment for the management of osteoporosis and associated conditions. The UK equine world has been slow to catch up and, although Tildren-use has been prevalent throughout Europe for a few years, until relatively recently it was only available in the UK on import license.

Also relatively recently, we have seen the release in the UK of Osphos, a new addition to the Bisphosphonate group. Osphos is licensed for use in horses with navicular syndrome.

How do Osphos and Tildren work?

Although the exact mechanism of action of bisphosphonates in horses is not completely understood, it is likely to be similar to that in humans. Normal bone is constantly being remodelled, with old bone being broken down by cells called osteoclasts and new bone being created by osteoblasts.

In normal healthy bone, the amount of bone being broken down will equal the amount of new bone being created. However disruption to this process causes an imbalance leading to bone loss and disease. This is what happens in Navicular syndrome and osteoarthritis.

Bisphosphonates such as Osphos and Tildren aim to decrease the action of osteoclasts, thus decreasing the rate of break down and resorption of bone. By decreasing the number and activity of osteoclasts, the osteoblasts are allowed to build new bone at the same rate at which it is being broken down.

Bisphosphonates bind with calcium, and the body’s calcium is stored in bone. As a result, bisphosphonates only accumulate in a high concentration in bone. They are incorporated into the bone matrix and are released slowly over time.

How do we administer Osphos and Tildren?

Even though they are in the same drug class, Osphos and Tildren have different methods of administration. Tildren is administered intravenously via a catheter, over the course of 90 minutes.  Osphos is administered via an intramuscular injection, with the dose being split over three different sites.

How long do the effects last?

It can take up to two months to see the full effect of a dose of Bisphosphonate. In the case of Osphos, a repeat dose can be given at 3-6 months if an improvement is seen. If the improvement lasts for longer than 6 months, then a second dose can be given as and when is necessary. The effects of a Tildren infusion may be seen for up to a year.

Are there any side effects?

Bisphosphonates can cause signs of colic in horses, such as abdominal pain, discomfort and agitation. However, these signs do tend to pass relatively quickly. Tildren and Osphos should be avoided in horses with impaired renal function; Tildren should not be given concurrently with non-steroidal anti-inflammatory drugs.


Evolution Vets will treat horses with either Osphos or Tildren when required. Osphos is routinely stocked and Tildren can be ordered for next day delivery. If your horse requires a Tildren drip please be aware that this process can take upwards of an hour as the drug must be given slowly via an IV catheter over a period of time.

If you would like more information then please don’t hesitate to give us a ring and speak to either Heidi or Ashley

Click to go to our Information sheet on Navicular Syndrome in Horses.