Clostridial myositis…Could your horse be at risk for this potentially deadly disease?

 I have advised clients on countless occasions against administering flunixin meglumine (commonly known as Banamine, Flunixamine, Flumeglumine, Flunixiject and Prevail) in the muscle to horses. While many take my advice, I always run across a few clients that are more resistant, explaining they have given this medication in the muscle for 20 years and never had a problem…. My response – it only takes one disaster and you’ll never give it in the muscle again.

During my career I have seen multiple horses die or euthanized due to complications from a serious secondary bacterial infection (Clostridial sp.) stemming from single or multiple intramuscular injections of flunixin meglumine. Interestingly, it is important to note that flunixin meglumine is labeled and FDA approved for intramuscular use in horses and certainly not every horse that recieves an injection in the muscle will develop an infection, but there is undoubtedly an inherent risk. Other medications have also been implicated in causing this serious infection when injected into the muscle including antihistamines, phenylbutazone, and anthelmintics (dewormers). These medications are irritating to muscle tissue when injected which may lead to focal tissue necrosis at the injection site. This is problematic because blood flow and oxygen (carried by red blood cells) is reduced in areas of devitalized tissue. Clostridial sp. require an absence of oxygen to thrive.

Clostridial spores are ubiquitous in the environment and are present on skin and hair even when it appears clean. When the needle is pushed through the skin into the underlying muscle tissue during an injection, Clostridial spores may be inadvertantly innoculated into the tissue. Spores can also be introduced through penetrating (puncture) wounds. Oftentimes this does not create a problem unless the conditions of devitalized tissue and low oxygen are present to support germination of the spores causing rapid widespread tissue necrosis and systemic toxemia. There are multiple Clostridium species present in the environment and any one of them can cause an infection. However, the severity of the infection is dependent on the species with C. sordelli the most deadly.

Clostridium bacteria causes local necrosis of muscle tissue and systemic toxemia through production of a multitude of toxins. Clinical signs develop rapidly (12-24 hrs) and include heat, pain, and palpable gas pockets (crepitous) under the skin at the site of injection. Typically, the horse has a fever and is depressed and inappetant. If the injection was given in the neck or hind leg, oftentimes the horse is reluctant to lift or turn its neck and may be lame.

Since this infection can be fatal, treatment should be instituted immediately and involves surgically opening up all pockets of fluid (abscesses) to expose the bacteria to air (oxygen) and debriding (removing) dead tissue. Aggressive antibiotic therapy is also instituted along with required supportive care. Prognosis for these cases depends on the Clostridial sp.(s) involved and the severity at the time treatment is initiated.

Prevention of this disease is far easier than treatment and many of the forementioned drugs have oral preparations available that are safe and effective.  The injectable liquid form of flunixin meglumine can also be safely and effectively administered orally. For my clients, I recommend administering flunixin meglumine orally if they are not confident in venipuncture.

As always, please consult with your veterinarian before administering any medications to your horse.


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