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Evaluation of the analgesic effects of phenylbutazone administered at a high or low dosage in horses with chronic lameness

Helen H. HuDepartment of Veterinary Clinical Sciences, College of Veterinary Medicine, Oklahoma State University, Stillwater, OK 74078.
Present address is 617 Stoney Spring Dr, Baltimore, MD 21210.

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Charles G. MacAllisterDepartment of Veterinary Clinical Sciences, College of Veterinary Medicine, Oklahoma State University, Stillwater, OK 74078.

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Mark E. PaytonDepartment of Statistics, College of Arts and Sciences, Oklahoma State University, Stillwater, OK 74078.

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Ronald S. ErkertDepartment of Veterinary Clinical Sciences, College of Veterinary Medicine, Oklahoma State University, Stillwater, OK 74078.

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Abstract

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 chronic lameness.

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)

Abstract

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 chronic lameness.

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)