Interleukin-1 receptor antagonist protein (IRAP) therapy

IRAP stands for interleukin-1 receptor antagonist protein, which is an anti-inflammatory product that the body produces. IRAP is known to counteract inflammatory damage in joints that is caused by osteoarthritis. IRAP can be manufactured from a horse’s blood, which is processed in a laboratory, before it is injected into a joint of the same horse.

IRAP is an autologous biological product because it is produced by the animal itself. For this reason it can only be re-injected into the same horse from which the blood to manufacture IRAP has been obtained. The final preparation also contains many other anti-inflammatory proteins in addition to IRAP, which may also be useful in combating osteoarthritis.

IRAP is used most commonly to treat joint inflammation that is not caused by infection. These may be cases of synovitis or cases of osteoarthritis. Cases of synovitis in which there is joint effusion (excess fluid within the joint), but no changes on radiographs (x-rays) may be ideally suited because the disease process is either in an early stage or mild, and the aim of the treatment is to slow down the inflammatory process as much as possible.

IRAP can also be very useful in combination with surgical treatments of joint diseases. If your horse undergoes arthroscopic (keyhole) surgery, your vet may recommend IRAP treatment based on the pre-operative findings, or may suggest administration once the joint has been inspected. IRAP is considered useful in cases where there is widespread cartilage and/or bone damage.

IRAP can also be injected into joints combined with steroids and/or antibiotics, which will not result in reduction of its therapeutic effect. It can also be used in horses that have already been treated with IRAP. In contrast to intra-articular steroid injections, there does not seem to be an adverse effect from repeated treatments.

The preparation will be manufactured by your vet.

Venous blood is collected from the horse’s jugular vein into a specially prepared syringe that contains cromium-soaked glass beads. Venous blood sampling from the jugular vein is well tolerated by most horses. However, if necessary, the skin over the jugular vein can be numbed with a local anaesthetic, or the horse can be lightly sedated. The syringe is then processed and warmed in an incubator, which results in increased production of IRAP and other anti-inflammatory proteins in the sample.

After 24 hours, the syringe is centrifuged to separate blood cells from the serum in the sample. The serum that contains the IRAP is then carefully collected and filtered before being divided between several smaller syringes for later injection into the joint(s). Usually, several doses of 3-5 ml each are prepared. Each IRAP production cycle yields a varying amount of serum, but usually it is possible to obtain 25-30 ml of serum, which is then divided into smaller individual doses.

IRAP can be kept frozen for at least 7 months. If necessary, vials stored in this manner can be defrosted and injected into the joint(s) of the same horse.

There is no set schedule with regards to number and frequency of intra-articular treatments with IRAP. An individual treatment plan will partially depend on how much IRAP has been produced, and how many individual doses have been made. Smaller joints require less IRAP. One production cycle will therefore yield more individual injections. Usually, IRAP is injected into the joint(s) every 7-14 days for a total of 3-4 treatments. IRAP injections can be combined with intra-articular steroids with no apparent detrimental effects.

As with any joint injection, there is always a risk of introducing infection. The procedure must therefore be performed under aseptic (sterile) conditions. Your vet may request that the procedure is done at a clinic to ensure the necessary safety precautions.

Following intra-articular injection, the joint will be placed in a support bandage. Depending on competition schedules, it is reasonable to say that a joint will respond better to IRAP if the horse has a week or two off work following treatment.