For decades, veterinarians have relied on non-steroidal anti-inflammatory drugs (NSAIDs) to manage both acute and chronic inflammation. Like most medications, NSAIDs have evolved over the years to become safer and more effective.
Equine veterinarians commonly use both nonselective and COX-1 sparing NSAIDs to treat pain and inflammation. A clear understanding of these mechanisms is essential for making informed treatment decisions.
Phenylbutazone
Phenylbutazone (bute) is the oldest NSAID still widely used in equine medicine. Introduced in human medicine in 1949, it was adopted for veterinary use in the 1950s. Decades later, it remains a cornerstone in the treatment of pain and inflammation from various sources, including osteoarthritis (OA). However, its potent analgesic and anti-inflammatory effects come with significant safety concerns. Chronic use is strongly associated with gastrointestinal ulceration, right dorsal colitis, and renal damage.
Flunixin Meglumine
The second-most used NSAID in horses is flunixin meglumine. Approved for equine use in 1977, flunixin is traditionally the NSAID of choice for soft tissue injuries, inflammation, and fever—particularly in conditions affecting the gastrointestinal tract, respiratory tract, and eyes. However, prolonged use can lead to renal toxicity and gastrointestinal ulceration. It has also been shown to delay intestinal mucosal healing.
Firocoxib
Firocoxib is the newest NSAID in equine medicine. It was approved in oral paste form in 2005 (Equioxx), followed by injectable and tablet forms and an oral solution in 2024 (Equicoxib). Known for its strong COX-1 sparing effects, firocoxib has a COX-1 to COX-2 binding affinity ratio of 1:250, in contrast to the 1:1 ratio of bute and flunixin. This high COX-2 selectivity allows firocoxib to effectively manage the clinical signs of OA while significantly reducing the risk of adverse side effects.
Efficacy of Firocoxib
Several studies support firocoxib’s efficacy in treating equine OA. In 2008, Doucet et al. conducted a study comparing firocoxib and phenylbutazone in 253 horses with naturally occurring OA-related lameness. After 14 days, 84.6% of horses treated with firocoxib and 86.6% of those treated with bute showed improvement, indicating comparable clinical efficacy.
In 2012, Orsini et al. studied 390 client-owned horses with OA-related pain and lameness across 80 sites. Investigators observed significant improvement in 78.7% (307/390) of cases over the 14-day treatment.
Safety Profile
Firocoxib’s most significant advantage over other NSAIDs may be its broad safety profile. In the original field efficacy study, only 0.03% treated at the label dose reported adverse events.
In a target animal safety study, horses were divided into three groups: One receiving the label dose for 30 days, another receiving 3X the label dose, and a third receiving 5X the label dose for the same period. No adverse effects were observed in the label dose group. The 3X and 5X groups experienced clinically significant oral lesions, and the 5X group showedclinical pathologic abnormalities.
Modern equine medicine depends on a small selection of approved NSAIDs to manage both acute and chronic pain and inflammation. Among the three most used options, firocoxib offers clinical efficacy comparable to phenylbutazone and flunixin meglumine but with a substantially better safety profile. As such, firocoxib represents a valuable advancement in the management of osteoarthritis in horses.
References:
- Tobin T et al. Phenylbutazone in the horse: a review” (1986). Maxwell H. Gluck Equine Research Center Faculty Publications. 94.
- Flood J, Stewart AJ. Non-Steroidal Anti-Inflammatory Drugs and Associated Toxicities in Horses. Animals (Basel). 2022 Oct 26;12(21):2939
- Marshall JF, Blikslager AT. The effect of nonsteroidal anti-inflammatory drugs on the equine intestine. Equine Vet. J. 2011;43:140–144
- Doucet, Michele Y, et al. Comparison of efficacy and safety of paste formulations of firocoxib and phenylbutazone in horses with naturally occurring osteoarthritis. JAVMA. 2008;232:1
- Orsini James A et al. Evaluation of oral administration of firocoxib for the management of musculoskeletal pain and lameness associated with osteoarthritis in horses. Am J Vet Res. 2012;73(5):664-71
- Freedom of information summary. NADA 141-253. Equioxx oral paste. 2005
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