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Effects of single-dose intravenous phenylbutazone on experimentally induced, reversible lameness in the horse


Dr Jonathan Foreman, Department of Veterinary Clinical Medicine, University of Illinois at Urbana-Champaign, 1008 West Hazelwood Drive, Urbana, IL 61802, USA. E-mail:


The objective was to test the hypothesis that phenylbutazone (PBZ) alleviates lameness in an adjustable heart bar shoe model of equine foot pain. Eight Quarter Horse mares underwent 4-weekly treatments randomly: 0.9% saline placebo (SAL: 1 mL/45 kg body weight i.v.) with no lameness; SAL with lameness; PBZ (4.4 mg/kg body weight i.v.) with no lameness; and PBZ with lameness. Blinded heart rate (HR) and lameness score (LS) were assessed every 20 min for 2 h and then hourly through 9 h. At 1 h SAL or PBZ was administered. Jugular venous samples were obtained at hours 0, 1, 2, 4, 6, and 8 and were evaluated for packed cell volume (PCV), cortisol, and drug concentrations. Repeated measures anova and t-tests were used to identify PBZ effects at a significance level of P < 0.05. PBZ-treated LS was lower 2–8 h post-treatment, and HR was lower from 2 through 6 h post-treatment (P < 0.05). Phenylbutazone did not change PCV and had minimal effect on cortisol. Mean plasma PBZ and oxyphenbutazone concentrations 7 h after treatment were 7.2–7.5 and 1.6–1.9 μg/mL, respectively. It was concluded that PBZ was efficacious in alleviating lameness in this model. Cortisol and PCV were not discriminating enough to distinguish between PBZ-treated and SAL-treated trials.