Tuesday, February 9, 2010

February 9, 2010 - Injectable Joint Therapies

Vet Tip of the Day: Injectable Joint Therapies
Key Words: Adequan, Legend, PSGAG, Hyaluronic Acid

To finish our segment on the hock, here is a brief discussion of the two FDA licensed injectable agents to improve joint health.  The first, Adequan, is used more commonly for osteoarthritis of the hock (bone spavin).  Adequan is a large molecule with the chemical name polysulfated glycosaminoglycan (PSGAG) which cannot be absorbed when given orally and so is administered by intramuscular injection.  Adequan has been shown repeatedly in controlled clinical trials to improve lameness associated with chronic degenerative joint disease, however, on an individual animal basis, it's effectiveness is quite variable.   Its mechanism of action is similar to chondroitin and glucosamine.  Remember that these oral supplements are building blocks used by the body in the construction of cartilage.  Adequan is a very large molecule, more complex than either chondroitin or glucosamine, and is further along the construction pathway in the formation of cartilage matrix.  The PSGAG molecule is incorporated into cartilage, giving it elasticity and shock abosorbing capacity.

I use the brand name Adequan, although there are generic PSGAG products available, as well as compounded products.  However, as with oral supplements, the molecular construction of the generics and compounded products are not necessarily equivalent to Adequan, and have not stood the test of clinical or experimental study.  In fact, Luitpold Pharmaceuticals, the manufacturer of Adequan, has spent quite a bit of money conducting quality research on their product, and in the comparison studies performed to date, Adequan has outperformed generics.  Once again, you get what you pay for.

Legend is injectable hyaluronic acid (HA).  And yes, just like PSGAG,  hyaluronic acid comes in many molecular weights and qualities, and so far, for intravenous administration, Legend is the gold standard.  While Adequan is used most commonly for hock arthritis, it is not uncommon to combine Adequan and Legend as joint therapies.  In the joint environment, hyaluronic acid and PSGAG have complex actions.  In addition to acting as structural components of joint fluid and cartilage, both HA and PSGAG have anti-inflammatory effects within the joint.  On top of that, when used together, each component enhances the activity of the other, so 1+1=3!  Therefore, in performance horses with joint issues, it may be advisable to use combination therapy. 

There is a standard protocol for initiation of Adquan therapy, established by the manufacturer.  The recommendation is to give 1 vial every 4 days for 28 days followed by one vial every 2-4 weeks thereafter. Legend is often given once monthly intravenously as maintenance therapy, with additional doses given around the time of competition.

Oral and injectable chondroprotectant agents are widely used in treating osteoarthritis of the hocks.  They often are used in conjunction with intra-articular (directly into the joint space) injections of similar products in combination with corticosteroids, as well as oral adminstration of non-steroidal anti-inflammatories such as phenylbutazone.  Finally, a topical anti-inflammatory cream is now available which provides local, temporary pain relief and can be effective to control hock pain during exercise.  This product is Surpass, or diclofenac acid.

We've covered a lot of information on the hock.  If you are interested in learning more,  use the key words provided as Search words in Google and you will find LOTS more to read.

Have a great day,

Ask a Horse Vet Online

We have partnered with JustAnswer so that you can get an answer ASAP.