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

This study evaluates the pain-relieving effects of two different doses of the drug phenylbutazone on horses with chronic lameness. The researchers found that a higher dose does not yield superior pain-relief compared to a lower dose, suggesting that the higher dose may not be needed and could potentially avoid unnecessary side effects.

Research Methodology

• The researchers conducted a controlled crossover study using nine horses which were all suffering from chronic forelimb lameness.
• The treatment administered to these horses included either a low dose of phenylbutazone (4.4 mg/kg/d), a high dose of phenylbutazone (8.8 mg/kg/d), or a saline solution (as a control group).
• All horses received each of the three treatments, with a minimum of a 14-day interval between each treatment cycle to prevent overlap or interference from one treatment to the next.
• Before each treatment cycle began, and at 6, 12, and 24-hour intervals after the final dose, the researchers measured each horse’s mean peak vertical force (mPVF) – a measure of the horse’s weight-bearing ability – and assigned a clinical lameness score to assess the severity of the horse’s lameness.

Results

• Compared to the saline solution treatment, both doses of phenylbutazone resulted in a significant increase in the mPVF and a significant decrease in lameness scores at all times of post-treatment evaluation.
• While both the high and low doses of phenylbutazone significantly reduced clinical lameness scores 6 and 12 hours after administration, reduction of lameness at 24 hours was only significantly observed when the high dose was used.
• However, there were no substantial differences between the low and high doses on both mPVF and clinical lameness scores at any of the assessment times.

Conclusions

• The researchers concluded that there was no significant difference in the pain-relief effect between the lower and higher dose of phenylbutazone.
• The study therefore suggests that the use of a higher dose of the drug may not offer additional benefits for chronically lame horses. This is particularly important because the toxicity of phenylbutazone is dependent on the dose – therefore, using a lower dose could possibly minimize side effects without compromising the analgesic effect.