Comparative evaluation of the analgesic effects of epidural morphine, alfentanil, butorphanol, tramadol and U50488H in horses.

This research project investigates and compares the pain-relieving effects of multiple drugs, when used in epidural analgesia, on specific regions of horses. The study suggests tramadol and morphine could be especially useful for long-lasting pain relief in the perineal and sacral regions of healthy horses.

Research Objective and Methodology

The aim of the study was to determine the efficacy of different drugs – morphine (M), alfentanil (A), butorphanol (B), tramadol (T), and U50488H (U) – used in epidural analgesia for horses. Epidural analgesia is a pain relief method through an injection in the spine. Five healthy adult horses received each treatment in a sequenced cross-over study, with seven days between each treatment. Treatments were administered and then followed by electrical stimulation, after which the threshold at which the horse showed avoidance behavior was measured.

• The treatments were administered at precise volumes and concentrations into the epidural space at a specific location on the horse’s spine.
• A gradually increasing electrical stimulation was administered at varied intervals after the treatment.
• The voltage at which the horse began to exhibit discomfort was then noted.
• These measurements were statistically analyzed including a two-way repeated measure analysis of variance and Bonferroni’s test.

Findings of the Study

The experiment found various results for the different drugs. B, U, and sterile water showed no change from the baseline threshold for electrical stimulation. Alfentanil did increase the threshold for pain, but the change wasn’t statistically significant.

• Tramadol significantly increased the pain threshold in the perineal and sacral regions shortly after injection, and this effect lasted for approximately 6 hours 40 minutes.
• Morphine also significantly increased the pain threshold in the same areas, but the effect took longer to appear and lasted for approximately the same duration.
• In the lumbar region, both Tramadol and Morphine were effective, with Tramadol acting faster and both treatments lasting for about 5 hours.
• Tramadol and Morphine both increased the pain threshold in the thoracic region, again with Tramadol acting faster. The effect of both treatments was shorter in this region, lasting approximately 3 hours.

Conclusion and Recommendations

The conclusion drawn based on the above findings is that both tramadol and morphine might be useful in providing long-lasting pain relief in horses, particularly in the perineal and sacral regions. Of the two, tramadol had a faster onset but morphine had a slightly longer duration. The results suggest that higher doses of alfentanil should be explored for epidural use in horses.