Effect of fentanyl on visceral and somatic nociception in conscious horses.
Authors: Sanchez L Chris, Robertson Sheilah A, Maxwell Lara K, Zientek Keith, Cole Cynthia
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary: Fentanyl's Limited Antinociceptive Effects in Conscious Horses Transdermal and intravenous fentanyl are increasingly employed in equine practice for pain management, yet robust evidence supporting their efficacy in horses remains limited. This study investigated whether intravenous fentanyl administration could raise visceral and somatic pain thresholds in six conscious horses equipped with gastric cannulae, using colorectal and duodenal distention to assess visceral nociception and thermal threshold testing for somatic pain. Despite achieving serum fentanyl concentrations (up to 7.82 ng/mL) that exceed those producing analgesia in other species, the drug failed to significantly elevate pain thresholds via either pathway—colorectal and duodenal distention thresholds remained unchanged, whilst thermal threshold showed only a modest, non-significant trend towards increased response at the highest dose, accompanied by agitation and tachycardia in two animals. These findings challenge the presumption that pharmacokinetic data from other species can reliably predict fentanyl's antinociceptive utility in horses, and suggest that clinicians should exercise caution when relying on fentanyl as a primary analgesic agent, particularly for visceral pain conditions where this study demonstrated no measurable benefit.
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Practical Takeaways
- •Transdermal fentanyl may have limited efficacy for visceral pain control in horses compared to other species, and alternative analgesic protocols should be considered
- •IV fentanyl administration in horses can cause adverse effects (agitation, tachycardia) that may limit clinical use despite adequate serum concentrations
- •Clinicians should be cautious about extrapolating fentanyl dosing from other species to horses, as equine response differs significantly from documented effects in other animals
Key Findings
- •Fentanyl IV administration did not produce significant antinociceptive effects on duodenal or colorectal distention thresholds in conscious horses
- •Thermal threshold showed an increased trend only at the highest fentanyl dose (mean serum concentration 7.82 ± 2.10 ng/mL) at 15 minutes
- •Two horses experienced agitation and tachycardia during initial fentanyl infusion despite serum concentrations exceeding nociceptive thresholds documented in other species
- •Fentanyl failed to demonstrate significant antinociceptive effects at doses that produce effective pain relief in other animal species