Efficacy of Phenylbutazone Versus Firocoxib in Experimental Lameness in Horses

Introduction There are few refereed blinded controlled documentations of skeletal analgesic efficacy of firocoxib, a selective COX ‐2 inhibitor. The objective was to test the hypotheses that intravenous firocoxib and phenylbutazone are comparable in efficacy and that both are more efficacious in alleviating lameness than placebo in an adjustable heart bar shoe model of equine foot pain. Methods Eight healthy adult horses (5 Thoroughbreds, 3 Quarter horses, mean age 8.3 ± 0.9 years, age range 4–13 years) underwent weekly intravenous treatments 1 hour after lameness induction. Treatments were isotonic saline placebo (1 ml/45 kg body weight), phenylbutazone (4.4 mg/kg), and firocoxib (label dosage 0.09 mg/kg). Treatments were randomly assigned and administered by co‐investigators who had no input on Heart Rate ( HR ) and Lameness Score ( LS ) measurements. Another investigator who was unaware of treatment assignments monitored HR and LS every 20 min for 5 hours after lameness induction and then hourly through 12 hours after treatment. One and two weeks later treatments were shuffled and the experiment was repeated. Repeated measures ANOVA and post hoc Tukey's test were used to identify analgesic effects at a significance level of P<0.05. Results HR and LS were not different between saline and firocoxib. Post‐treatment phenylbutazone HR (2.3–3.3, 5, and 10 hours) and LS (2.3–8 hours) were lower than saline (P<0.05). Phenylbutazone HR (10 and 12 hours) and LS (1.67–11 hours) were lower than firocoxib (P<0.05). Conclusions It was concluded that firocoxib at this label dosage was not different than placebo and that phenylbutazone was more effective than firocoxib and saline. Ethical Animal Research Study approved by the University of Illinois Institutional Animal Care and Use Committee. Sources of funding:  Fédération Equestre Internationale. Competing interests:  none.