Page 934 - Adams and Stashak's Lameness in Horses, 7th Edition

900 Chapter 8

ORAL/NUTRITIONAL

VetBooks.ir nicoLaS S. ernST anD Troy n. TrumbLe

Lameness is one of the most prevalent diseases, which producing prostaglandins involved in normal physiologi-
affects the equine industry. It is considered the most cal functions such as gastric and renal function and hemo-
common and important performance‐limiting problem stasis. The COX‐2 isoenzyme is considered to be an
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in horses. This section discusses oral formulations used important inducible mediator of inflammation in several
to treat the causes of lameness. Specifically, it focuses on organs and is primarily responsible for the inflammatory
oral formulations of nonsteroidal anti‐inflammatory pathway. However, the concept that COX‐2 is purely
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drugs (NSAIDs) and the most common compounds used involved in inflammation has changed since the COX‐2
in equine nutraceuticals. isoenzyme has been found to be constitutively formed in
the brain, spinal cord, kidney, uterus, and some other
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regions. In fact, one study demonstrated that in vol-
NONSTEROIDAL ANTI‐INFLAMMATORY DRUGS ume‐depleted horses a COX‐2 preferential agent (meloxi-
cam) had similar adverse renal effects as the nonselective
NSAIDs are a large group of drugs with differing NSAID, phenylbutazone (PBZ). 117
degrees of analgesic, anti‐inflammatory, and antipyretic The variation in efficacy and toxicity of the different
properties (Table 8.3). In a survey of horse owners and NSAIDs is closely related to inhibition of the different
trainers, 96% of respondents stated that they use NSAIDs, COX isoenzymes (Table 8.3). Some are more potent
and 82% said they administer them without consulting a inhibitors of COX‐1 than COX‐2, some equally inhibit
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veterinarian. However, NSAIDs are also heavily pre- both, and others inhibit COX‐2 more than COX‐1. In
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scribed by veterinarians as demonstrated in an observa- general, the anti‐inflammatory and analgesic properties
tional study of multiple practices in multiple countries of NSAIDs are believed to be mainly due to inhibition of
where clinicians prescribed NSAIDs in the United States the inducible COX‐2, whereas the adverse effects seem
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(42.4%) more than those in Canada (34.2%), or in the to be caused by inhibition of the constitutive COX‐1.
United Kingdom (28.6%). Oral formulations come in This has led to the development of NSAIDs with a selec-
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many varieties such as pills, paste, granules, and powder, tive inhibition of COX‐2. In humans, COX‐2‐selective
allowing the consumer to choose which formulation is inhibitors demonstrated adverse cardiovascular and
best for each individual. Some of these medications can thromboembolic effects, but horses do not appear to be
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also be administered systemically via intramuscular or predisposed to these adverse effects. It is also impor-
intravenous injection (Table 8.3). In general, NSAIDs act tant to note that COX‐2 selectivity is only achieved
by inhibiting cyclooxygenase (COX) enzymes that con- when administered at correct dosing; overdosing can
vert arachidonic acid into prostaglandins and thrombox- lead to similar adverse effects of nonselective NSAIDs. 165
anes. There are two well‐known isoenzymes of the COX Recommendations for NSAID usage should be for-
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enzymes, COX‐1 and COX‐2. In general, COX‐1 is mulated in attempt to minimize adverse effects when it
considered the housekeeping isoenzyme responsible for is determined that an oral NSAID may be a beneficial
Table 8.3. Commonly used NSAIDs and their modes of action, formulations, and doses for equine musculoskeletal disorders.

Name of NSAID Primary inhibitory action Available formulations Recommended dose
Phenylbutazone Cox‐1 and ‐2 Powder, tablets, paste, and injectable solution 2.2–4.4 mg/kg SID or BID

Flunixin meglumine Cox‐1 and ‐2 Paste, granules, and injectable solution 1.1 mg/kg SID
Acetylsalicylic acid Cox‐1 > Cox‐2 Gel, powder, granules, paste, and tablets 25–35 mg/kg SID or BID
Meclofenamic acid Cox‐1 and ‐2 Granules 2.2 mg/kg SID for 5–7 days
Naproxen Cox‐1 and ‐2 Granules, tablets, and suspension 10 mg/kg SID or BID
Firocoxib Cox‐2 Paste, injectable solution, and tablet 0.1 mg/kg SID, 0.09 mg/kg SID IV

Carprofen Cox‐2 > Cox‐1 Tablets and injectable solution 0.7 mg/kg SID
Vedaprofen Cox‐2 > Cox‐1 Gel and injectable solution 2 mg/kg loading dose followed by
1 mg/kg q12 h
Meloxicam Cox‐2 > Cox‐1 Suspension, injectable solution, oral solution, 0.6 mg/kg SID
and tablets