Analgesic effects of epidural administration of hydromorphone in horses.

This study evaluates the pain-relieving effects of hydromorphone, administered via the epidural route, in different body regions of horses. The research indicates that epidural hydromorphone significantly increases the threshold at which horses respond to painful electrical stimulation for a duration of 250 minutes post-administration, suggesting its potential usefulness in managing moderate to mild pain in horses.

Study Methodology

• The study involved six healthy adult horses.
• The two groups formed were administered either hydromorphone (0.04 mg/kg) or sterile water (control solution) in the first intercoccygeal space. Each treatment was administered at least 7 days apart.
• Noxious electrical stimulation was applied to the perineal, sacral, lumbar, and thoracic regions (dermatomes) for a duration of six hours following epidural injection. The voltage, at which the horses responded (avoidance threshold), was noted.

Study Findings

• Sterile water did not alter the avoidance threshold, as expected in a control solution.
• Hydromorphone resulted in a significant increase in the avoidance threshold as early as 20 minutes post-injection, lasting till 250 minutes post-injection. This phenomena was observed across all stimulated regions – perineal, sacral, lumbar, and thoracic.
• Profound analgesia, defined here as an avoidance threshold greater than 40 Volts, was only noticed in the perineal region at 60 minutes post epidural administration of hydromorphone.
• The level of analgesia across all dermatomes was considered moderate for a duration of 250 minutes post-injection.

Conclusion

• Epidural administration of hydromorphone increased the avoidance threshold to painful stimulation in horses across multiple body regions. This effect lasted for approximately 250 minutes post-administration.
• The findings propose the potential application of epidural hydromorphone in managing pain of moderate to mild intensity in horses.