Page 936 - Adams and Stashak's Lameness in Horses, 7th Edition

902 Chapter 8

and prolong bleeding time in horses with doses between higher C , shorter T , greater area under the concentra-
max
max
12 and 24 mg/kg. 16,70,141 These effects can occur after a tion curve (AUC), and greater inhibition of prostaglandin
VetBooks.ir caution should be used and close monitoring performed of different doses of firocoxib in horses with chronic lame-
E (PGE ) when compared with the tablets. The efficacy
Therefore,
single dose and can last as long as 48 hours.
60
16,70
2
2
ness was assessed using objective assessment with a force
when using this drug on horses before surgery or with
bleeding tendencies or anemia. Due to its effect on plate, showing that a dose of 0.1 mg/kg orally once a day
platelets, aspirin has been historically used for the treatment was found to be most effective in reducing chronic lame-
97
of navicular syndrome and chronic laminitis. However, ness in horses. When administering this oral dose (0.1 mg/
3
its therapeutic benefits for these diseases are not well kg SID) over multiple days, it has been shown that it can
defined. take up to 7 days to reach steady state. However, if a
85
loading dose (0.3 mg/kg) is administered 24 hours before
Meclofenamic Acid (Arquel) starting a multidose regimen at 0.1 mg/kg, the steady‐state
concentration of the drug can be achieved after the first
Meclofenamic acid (MA) is another oral nonselective day of treatment. 26
NSAID used to treat lameness and chronic musculoskel- In a study of horses with chronic OA and navicular
36
etal conditions such as navicular disease, OA, and lami- syndrome, no significant differences in clinical improve-
nitis in horses. Compared with other NSAIDs, MA has ment were found between horses treated for 14 days
25
a slow onset of action of 36–96 hours for full effect. It with firocoxib compared with PBZ treatment. However,
25
is not clear whether feeding time dramatically affects a greater proportion of horses treated with firocoxib
absorption because one study demonstrated that fasted had improvement in scores for pain on manipulation
and nonfasted ponies had similar oral absorption, or palpation, joint circumference, and range of motion
131
whereas another study demonstrated that plasma levels compared with PBZ. In another study of a large number
could be delayed by feeding. The reported bioavaila- and cross section of horses with musculoskeletal pain or
136
bility after oral administration varies between 56% and lameness associated with OA, firocoxib paste signifi-
90%. 68,131 MA may prove to be useful for OA because cantly improved lameness scores, comfort, and mobility
high levels can be found in synovial fluid and articular in horses with the most change occurring within the first
cartilage. High doses produced clinical signs of toxic- 7 days of treatment. 112
25
ity similar to those of PBZ (at a dose 13–18 mg/kg). 84,138 Compared with other nonselective NSAIDs, firocoxib
is relatively safe. No clinical and biochemical signs of
Naproxen (Equiproxen, Naprosyn) NSAID toxicity were reported when using the recom-
mended dose (0.1 mg/kg). A pharmacokinetic and
43
Naproxen is a nonselective NSAID with analgesic and safety study was performed in neonatal foals, where 36‐
antipyretic properties that has been used primarily to hour‐old neonates received 0.1 mg/kg orally SID for 9
treat myositis and soft tissue problems. 27,138 In a study days; it showed that firocoxib was rapidly absorbed
using an equine myositis model, oral naproxen was with no reportable adverse effects. In a postoperative
63
reported to be superior to oral PBZ, with faster relief of ex vivo study, firocoxib action on COX‐2 was similar to
inflammatory swelling and associated lameness. After flunixin meglumine in that they both prevented its
69
oral administration the bioavailability of the drug is increase 24 hours after surgery; the firocoxib group
approximately 50% with peak plasma levels reached at demonstrated a sparing effect of COX‐1 activity with
3–4 hours; the plasma half‐life is approximately 4 greater activity than flunixin. However, it has been
38
hours. Naproxen has a wide margin of safety. Oral reported that an oral dose of 0.1 mg/kg SID for 10 days
138
administration of four times the recommended dose for can still develop gastric ulceration, but the severity of
42 days did not cause signs of toxicity. In another the ulceration being less severe than with PBZ adminis-
138
study, administration of the recommended dose of nap- tration (4.4 mg/kg PO SID). In addition, co‐adminis-
121
roxen for 14 days, followed by twice the dose for another tration with another NSAID can eliminate the benefit of
133
7 days, did not alter plasma protein concentrations. the COX selectivity; adverse renal issues were present
Even though this drug has been marketed for soft tissue when oral firocoxib (0.1 mg/kg SID) was combined with
79
conditions, successful usage in the human field for treat- oral PBZ (2.2 mg/kg SID) for 10 days. For this reason,
ing joint pain may suggest that it can be used to treat some equine governing bodies are no longer permitting
inflammatory swelling and associated lameness. 69,97 the combination use of firocoxib with other NSAIDs. 165
The main downfall to firocoxib is that it is more expen-
Firocoxib (Equioxx ) sive than PBZ. Therefore, the economic feasibility must be
®
discussed with the client. This can often lead to off‐label
Firocoxib is a COX‐2‐selective NSAID that has been use of the chewable canine tablets by owners due to the
approved by the FDA for controlling pain and inflamma- substantial difference in cost between the formulations for
tion associated with OA in horses. The bioavailability the different species. Because of this, one study examined
after oral administration in horses is 79%, with a time to the effect of 57 mg of the canine tablet or the equine paste
5
peak concentration of 3.9 hours and elimination half‐life administered orally to horses for 7 days. The collected
of 30 hours. 60,80,81,85 It is metabolized in the liver and blood was challenged with lipopolysaccharides (LPS) to
excreted in the urine. It is well distributed in the body, induce PGE There was no difference between formula-
85
2.
including synovial fluid, liver, fat, kidney, and muscle. tions in reducing PGE production or in plasma firocoxib
2
Firocoxib is available in two oral formulations (paste concentrations. Therefore, they conclude that tablets may
and tablets). When a single dose of 57 mg was administered be viable option if extra‐label use can be justified, but it is
5
to 6 horses, the paste revealed a better bioavailability, important to note that one cannot legally prescribe the