Effect of fentanyl on thermal and mechanical nociceptive thresholds in horses and estimation of anti-nociceptive plasma concentration.

The research article investigates the relationship between administered doses of fentanyl and its resulting anti-pain effects in horses, as well as identifying the minimum pain-relieving plasma concentrations.

Research Objectives and Methodology

• The research aims to investigate the analgesic (pain-relieving) efficiency and duration of fentanyl in horses and to determine the minimum plasma concentrations at which fentanyl becomes effective in reducing pain.
• Eight horses were treated with saline and varying doses of fentanyl, administered intravenously over a period of 5 minutes, with a ten-day wash-out period between drug administrations.
• The study evaluated both the horses’ thermal (heat) and mechanical (pressure) pain thresholds. Single stimulations were applied before treatment and at varying intervals thereafter, up to 22.5 hours post-treatment.
• The concentrations of fentanyl in the horses’ plasma were measured at specific time points.
• In addition to pain thresholds, the researchers also recorded locomotor activity, as well as heart rate, respiratory rate, and gastrointestinal sounds of the horses. They used two-way repeated measures ANOVA and pairwise comparisons for data analysis.

Key Findings

• A significant increase in thermal pain threshold above the baseline was observed at certain time points with the certain doses of fentanyl. It leads to an increase in the horse’s capacity to withstand higher temperatures before indicating discomfort.
• The mechanical pain threshold showed a considerable increase only at certain time points, suggesting an increased resistance to pressure-based pain.
• The minimum effective plasma concentration determined by thermal stimulation was between 6.1-6.8 nanograms/milliliter.
• A dose-dependent increase in movement activity was observed, but no significant changes in other physiological parameters, including heart rate, respiratory rate and gastrointestinal sounds, were noted.

Conclusion

• From the study, it was inferred that an intravenous fentanyl dose of 10 micrograms/kilogram produced effective pain relief for 10-30 minutes in horses.
• It was also found that the necessary plasma concentration for inducing thermal pain relief ranges from 6.1 to 6.8 nanograms per milliliter.
• The primary side effect noted was a dose-dependent increase in locomotor activity, suggesting the horses moved around more with increased dosage.