Adequan and Legend
Matt Evans, DVM

Adequan and Legend In recent years veterinarians have made substantial progress in the field of equine lameness and osteoarthritis. As our knowledge of osteoarthritis has increased, so have the number of treatment options. In addition to traditional non-steroidal anti-inflammatories (i.e. Phenylbutazone) and corticosteroids, use of new drugs that supplement naturally occurring joint substances is now common. Hyaluronic Acid (HA) and Polysulfated Glycosaminoglycans (PSGAG) are the two primary new medications that veterinarians are using to treat osteoarthritis at this time. Both are used as intra-articular injection and both are available as systemic medications; HA as Intravenous Legend and PSGAG as Intramuscular Adequan.

The use of IV Legend and IM Adequan in the equine athlete raises many questions for owners and trainers to consider. What, exactly, are HA and PSGAG? How do they work? Are they safe? How are they similar and different? Should they be used as a treatment, a preventative or both?

First a note on the term osteoarthritis: it is described as “dynamic” ­ a continually changing disease process. A horse’s joint does not become arthritic in one day; the state of a diseased joint is a point on a continuum. Our goals in treating the patient are contingent upon knowledge of where this patient is in the disease process. Accurate diagnosis is imperative to making a correct decision as to which medications and treatments are correct for your horse.

HA and PSGAG are similar compounds found in normal equine joints. HA is a linear polydisaccharide and a polyionic nonsulfated glycosaminoglycan. It is an important part of normal synovial (joint) fluid and articular cartilage. HA is normally synthesized by synoviocytes and adds viscosity and elasticity to the joints. As an aside, HA is also found in the heart, eyes and skin. PSGAG is also a polysulfated glycosaminoglycan and is comprised mainly of chondroitin sulfate. PSGAG is a normal constituent of articular cartilage. (The above passage, if memorized and verbalized at just the right moment, will place you in high esteem with your fellow riders.)

HA’s method of action is uncertain but several rational hypotheses exist. The HA is believed to collect at the synovial membrane and bind to HA cell receptors inhibiting inflammation in that area. PSGAG’s method of action is likewise uncertain. It is known that PSGAG inhibits many enzymes associated with cartilage damage as well as inflammatory enzymes. It is possible PSGAG may also stimulate endogenous HA synthesis.

Both IV HA and IM PSGAG have been proven in clinical trials to decrease lameness and inflammation in clinically lame horses. There are no current studies that definitively prove that either drug acts as a prophylactic and prevents lameness from occurring, though research trends are suggestive. Neither HA nor PSGAG have shown any demonstrable side effects when given in their recommended forms.

With the above information it is natural to conclude that IV HA and IM PSGAG are viable treatment options for the horse that is already showing signs of osteoarthritis in one or more joints. Since both drugs decrease inflammation by inhibiting enzymes that are associated with osteoarthritis they are both good choices for the sound horse or the horse in very early arthritis (mild synovitis). The chondroprotective aspects of PSGAG make it a good choice if mild to moderate cartilage damage is suspected.

The above information should act as a useful guide as you evaluate these medications for your horse. Although definitive research is not available in all areas, the safety and effectiveness of these medications make them excellent treatment options for the performance horse. The ultimate decision should be made with your veterinarian, weighing all aspects of your horse’s condition and athletic pursuits.

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