We are now aware of the many deleterious side effects of NSAIDS in the horse.  The nonspecific COX inhibitors such as phenylbutazone, ketoprofen, and flunixin meglumine can cause gastrointestinal ulceration and renal dysfunction.  These NSAIDS work by blocking prostaglandin production throughout the body.  Blockage of prostaglandins results in decreased inflammation and pain, which is the desired effect.  Unfortunately, blocking prostagladin pathways also results in decreased blood flow to some parts of the body, including the lining of the gastrointestinal tract and the kidneys.  This result in damage to the tissues and can lead to GI ulcers and decreased kidney function or failure.  The COX-2 inhibitor firocoxib is designed to lessen the potential effects on the GI tract and kidneys, but it is also not without some potential side effects.  

The pharmaceutical companies have spent many years and many millions of dollars to develop these drugs and to determine the correct dosages and dosing schedule for them.  These dosages are formulated to maximize the positive effects, i.e. pain management for NSAIDs, and to minimize the negative side effects. 

When it comes to NSAIDs, more is not better.  Altering the dosage, the dosing schedule, or combining two NSAIDs can prove to be harmful.  A recent study performed by Dr. Jonathan Forememan and Dr. Rebecca Ruemmler at the University of Illinois set out to determine the efficacy of phenylbutazone, flunixin meglumine, and a combination of  the two on experimentally induced lameness in horses.  They used eight horses in the study and over a four week period treated each with intravenous phenylbutazone, saline control, flunixin meglumine, or a combination of phenylbutazone+flunixin meglumine  at label dosages one hour after inducing lameness.  The horses were monitored for lameness score and heart rate for twelve hours after the lameness was produced. Blood samples for drug level were taken as well.  The results of the study showed that phenylbutazone alone decreased the lameness score the fastest; that all NSAID treatments decreased heart rate up to ten hours post treatment compared to the saline placebo; and that there was no difference between the flunixin meglumine and phenyulbutazone+flunixin meglumine groups through the entire twelve hours post treatment.  Another recent study showed that even just a few days of flunixin meglumine+half dose of phenylbutazone will cause gastric ulceration.

The take home message is that only one NSAID is needed to treat lameness and that combining more than one will not improve the lameness any more than either drug alone, but you do greatly increase the risk for GI or kidney damage.

Horse owners need to be aware that using NSAIDs in combination is now forbidden under United States Equestrian Federation (USEF) regulations.  A rule change that went into effect December 2011 states that horses competing in USEF sanctioned events may use only one NSAID while competing.  If a horse is found to have more than one NSAID in their blood, disciplinary action will be taken.  This rule change was made to protect the welfare of the horse.

There are certain situations where a second NSAID may be called for.  For instance, a horse who receives bute prior to competing that then incurs a minor corneal ulcer,  Flunixin meglumine could be administered in this case.  If the horse were fit enough to show, paperwork could be filed with the show steward and the horse allowed to compete.  These are very specific instances, and the welfare of the horse should be of utmost importance.

All NSAIDs are forbidden under Fédération Equestre Internationale (FEI) regulations.

Registered 2012 Equestrian Collections; Author: Sallie S. Hyman, VMD, DACVIM, CVA  

Information in this article is for educational purposes only and is not a substitute for evaluation by an equine professional.  In particular, all horse owners should seek advice  and treatment from a licensed veterinarian for their horses' medical care.  


Please check with your show associations for any rules or regulations regarding drug usage.  This article is for informational purposes only, and should not be considered an authoritative document on drug usage during competition.