Page 935 - Adams and Stashak's Lameness in Horses, 7th Edition

Principles of Therapy for Lameness 901

treatment option. In general, oral NSAIDs should be renal blood flow and/or direct toxic effect of the drug or
used at the lowest effective dose and frequency as pos- its metabolites. 84,117 Because of this narrow margin of
VetBooks.ir tion should be used when treating susceptible breeds alternative therapies should be considered when horses
safety and adverse effects, special considerations or
sible, for the shortest period of time. Special considera-
require long‐term administration. Often in severely
(ponies), foals, and systemically ill, dehydrated, or old
horses. NSAIDs are commonly used in performance affected orthopedic cases, horses can be safely main-
horses for recovery of minor injuries. However, most tained on 2.2 mg/kg/day of PBZ for months when gas-
sport horse disciplines have rules about using NSAIDs troprotectants are used concurrently.
before or during competitions. See each individual gov- Combination of oral PBZ with other NSAIDs may
erning body for guidelines regarding appropriate thera- enhance the analgesic properties of these drugs in perfor-
peutic use of NSAIDs for that discipline. mance horses. 74,120 Some studies have shown a better
clinical improvement in lameness when a combination of
Phenylbutazone (Butazolidin®, Butatron™, Bizolin®, drugs is used than when PBZ is used alone, 74,120 whereas
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Phenylbute™, Phenylzone®, Equiphen®, Butequine®, others have not. Caution should be used when combin-
Superiorbute®, and Equizone 100™) ing NSAIDs to minimize the potential toxic effects.
PBZ is an acidic, lipophilic NSAID that is classified as ®
an enolic acid and is metabolized in the liver and excreted Flunixin Meglumine (Banamine )
in the urine. Following oral administration, PBZ is well Flunixin meglumine is a derivative of nicotinic acid
absorbed in the stomach and small intestine. The that exhibits analgesic, anti‐inflammatory, and antipy-
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plasma half‐life after oral administration has been retic activity. After oral administration the drug is rap-
reported to be between 6.2 and 6.7 hours. However, idly absorbed with a peak in plasma levels within 30
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absorption can be influenced by the drug’s formulation minutes, and the plasma half‐life is approximately 1.6
and the route of administration. 4,75 For example, the hours. This rapid absorption may be important in min-
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paste formulation offers a greater rate and extent of imizing potential ulcerogenicity. The onset of action
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absorption than tablet or powder formulations, and after oral administration occurs after 2 hours, with the
peak plasma concentrations and onset of action can be greatest effect between 2 and 16 hours; some activity
delayed by administration close to feeding. may persist for up to 30 hours. Similar to PBZ, recent
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Oral PBZ is an inexpensive NSAID that has potent feeding delays absorption. Oral administration of flu-
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pain relief, antipyretic, and anti‐inflammatory proper- nixin is relatively safe. In one study, three times the rec-
ties. It provides pronounced analgesia and reduction in ommended dose given orally for 15 days failed to induce
inflammation in many common lameness problems, toxic effects. However, oral administration of flunixin
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including naturally occurring chronic osteoarthritis at 1.1 mg/kg/day for 30 days in foals resulted in oral and
(OA). It is often administered prior to surgery to mini- gastric ulceration. In addition, high doses for long
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mize pain and inflammation associated with orthopedic periods can cause GI intolerance, hypoproteinemia, and
surgical procedures. However, studies have demon- hematological abnormalities.
strated that oral PBZ may have negative effects on carti- Oral flunixin meglumine can be used to treat muscu-
lage and bone metabolism. A study in healthy horses loskeletal disorders in horses, but because of its cost
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receiving oral PBZ reported a decrease in bone activity compared with PBZ, oral formulations are used infre-
(decrease in mineral apposition rate and a reduction in quently. In general, oral flunixin has been used mostly to
the magnitude of healing) compared with horses not treat musculoskeletal injuries associated with soft tissue
receiving PBZ. In another study, PBZ administered structures such as muscle and tendons. However, there
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(4.4 mg/kg) orally twice daily for 14 days to healthy are no studies indicating that it is better or worse than
horses resulted in significant decreases in proteoglycan other NSAIDs at controlling pain and inflammation
synthesis by suppressing chondrocyte metabolism in associated with the musculoskeletal system. When flun-
articular cartilage explants. Recovery of chondrocyte ixin is combined with other NSAIDs, some studies have
8
metabolism took 2 weeks to normalize after cessation of shown enhanced analgesic properties of these drugs in
treatment. In contrast, no significant adverse effects performance horses compared with when used alone, 74,120
were identified using systemic cartilage and bone bio- whereas others have not. 47
markers when PBZ (4.4 mg/kg) was administered orally
twice daily for 3 days followed by a lower dose (2.2 mg/
kg) for 7 days in healthy horses. 48 Acetylsalicylic Acid (Aspirin)
Oral PBZ has been widely studied for its toxic effects Aspirin is a weak acid that reduces platelet aggrega-
on horses. It is considered relatively nontoxic at repeated tion and has analgesic, anti‐inflammatory, and antipy-
doses of 2.2 mg/kg twice a day or less. Clinical signs retic properties. It is only available in oral forms and
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reported with PBZ toxicity in horses are anorexia, has a limited clinical use in the horse. It is best absorbed
depression, loss of weight, abdominal edema, hypopro- in the acidic environment of the upper GI tract. In
teinemia, leukopenia, anemia, and death within 4–7 ponies, oral administration of salicylate demonstrated
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days. The gastrointestinal (GI) tract is the most com- rapid absorption with a peak in plasma levels within an
monly affected area following oral administration, caus- hour, with the highest concentrations of drug attained
ing ulcers (oral, esophageal, gastric, cecal, and right in the liver, heart, lungs, renal cortex, and plasma.
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dorsal colon) and a protein‐losing enteropathy. Renal Aspirin affects platelet function at low dose rates,
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papillary necrosis has also been described and may be reducing clotting times and thrombus formation.
16
due to the inhibition of prostaglandins that maintain Aspirin has been reported to decrease platelet numbers