Objective—To compare analgesic effects of phenylbutazone
administered at a dosage of 4.4 mg/kg/d
(2 mg/lb/d) or 8.8 mg/kg/d (4 mg/lb/d) in horses with
Design—Controlled crossover study.
Animals—9 horses with chronic forelimb lameness.
Procedure—Horses were treated IV with phenylbutazone
(4.4 mg/kg/d or 8.8 mg/kg/d) or saline (0.9%
NaCl) solution once daily for 4 days. All horses
received all 3 treatments with a minimum of 14 days
between treatments. Mean peak vertical force (mPVF)
was measured and clinical lameness scores were
assigned before initiation of each treatment and 6, 12,
and 24 hours after the final dose for each treatment.
Results—Compared with values obtained after
administration of saline solution, mPVF was significantly
increased at all posttreatment evaluation times
when phenylbutazone was administered. Clinical
lameness scores were significantly decreased 6 and
12 hours after administration of the final dose when
phenylbutazone was administered at the low or high
dosage but were significantly decreased 24 hours
after treatment only when phenylbutazone was
administered at the high dosage. No significant differences
in mPVF and clinical lameness scores were
found at any time when phenylbutazone was administered
at the low versus high dosage.
Conclusions and Clinical Relevance—Results suggest
that the high dosage of phenylbutazone was not
associated with greater analgesic effects, in terms of
mPVF or lameness score, than was the low dosage.
Considering that toxicity of phenylbutazone is related
to dosage, the higher dosage may not be beneficial in
chronically lame horses. (J Am Vet Med Assoc 2005;226:414–417)