Pentosan vs. Adequan vs. Legend for Joint Maintenance
Many horses either because of competition demands or the inevitable results of aging require joint medications to keep them in prime performance. The best approach if a specific joint is involved is to do direct joint injections. In addition to direct injections, systemic intravenous (IV) or intramuscular (IM) joint medication can help maximize the response and extend the time between when direct joint injections are needed. These maintenance medications are given on an ongoing basis in many cases. In order to prevent joint disease or delay its onset, they are used prophylactically in horses without any obvious joint disease but where they are at risk of developing joint problems because of their athletic demands.
The three most used medications are Legend®, Adequan® and Pentosan combined with Acetyl-D-Glucosamine
Pentosan with Glucosamine
Pentosan is a joint medication that can be administered by intramuscular injection. It has been in use in the USA for about a decade and longer in other parts of the world. It positively affects joints in several ways. Pentosan -
Stimulates the cells inside of joint cartilage to make more cartilage
Stimulates the cells in the joint capsule to make high quality hyaluronic acid. This is a major component of joint fluid that helps lubricate the joint.
Inhibits the release of enzymes that breakdown cartilage and inhibits inflammatory molecules
Has an anti-inflammatory action
Helps break down clots in the joint and in the vessels below the cartilage
In a study multiple horses had a bone chip arthroscopically created in their knee. Following the surgery, the horses were exercised to create inflammation and arthritis. The group that was treated with Pentosan had less cartilage breakdown, less lameness and greater joint flexion. The primary researcher, Dr. McIlwraith, who is a luminary among equine veterinary researchers, felt the positive response in the horses in this experiment to pentosan implied “superiority of this product to intramuscular Adequan” which did not show much effectiveness in the same type of experiment. These results have led me to prefer Pentosan with Glucosamine to Adequan as a maintenance joint medication.
I recommend a loading dose once a week for four weeks, then twice a month as maintenance. It is often takes until the 3rd or 4th injection before clients will notice a difference in their horse.
Adequan
Adequan as a joint medication has been available since the 1980’s. The active ingredient is PSGAG also known as chondroitin sulfate. Using Adequan for in the joint injections has been shown to help joint disease. However when used systemically by intramuscular shots in an experiment where knee joints had a chip created, it showed little impact.
Supporting the use of Adequan as a maintenance joint medication is one study in a non-peer reviewed journal. Quarter Horse race horses used Adequan over the course of a race meet with another similar group not using it. The treated horses received two injections per week for four weeks every other month. The horses treated with Adequan had significantly more earnings and more starts than the non-treatment group.
Adequan is typically given as a 7 dose series every 4 days as a loading dose, then at least twice a month after that. As an alternative the every other month 7 dose series can be used as it was in the study above.
Legend
Legend is a form of hyaluronic acid (HA) given IV. HA has been used for since the 1980's in direct joint injections commonly in combination with corticosteroids. Given IV in the form of Legend it has been shown to have some value reducing an inflamed joint - called synovitis.
While IV Legend is widely used as a maintenance joint medication there is actually limited scientific evidence to support that use. There has been only one study to look specifically at this in racehorses. The authors did see the treated horse earn more money over the treatment period however, the horses in the treatment group had a greater number of joint injections and greater use of Adequan than the non-treatment group making it hard to parse out what contribution the use of Legend had to their higher earnings.
Legend is given IV with a loading dose is 1 injection per week for 3 weeks and maintenance is 1 injection per month.
A word about oral joint treatments
Unfortunately, equine joint disease research has shown little if any benefit in horses to oral joint treatments with products containing Chontroiten Sulfate or Glucosamine. A possible reason is these large molecules are broken down into their simpler building blocks and so not absorbed in great amounts.
To paraphrase one researcher, if directed joint injections are a 9 or 10 in terms of effectiveness, then systemic medications might be a 4 or 5 and oral treatment a 0 or 1.