Effect of fentanyl on visceral and somatic nociception in conscious horses.
BACKGROUND
Transdermal fentanyl is used clinically in horses based on pharmacokinetic data and antinociceptive effects documented in other species.


OBJECTIVE
Fentanyl IV administration increases both visceral and somatic nociceptive threshold in conscious horses.


METHODS
Six clinically normal horses, each fitted with a permanent gastric cannula.


METHODS
Visceral nociception was evaluated with 2 methods of threshold detection--olorectal distention and duodenal distention. Somatic nociception was assessed by measurement of thermal threshold. Fentanyl was administered as an increasing stepwise infusion followed by a continuous-rate infusion for a total of 2 hours. There were 4 doses of fentanyl and 1 dose each of saline and xylazine administered to each horse. Serum fentanyl concentrations were measured and the resulting data were used to determine pharmacokinetic parameters for each horse. All data were analyzed by means of a 3-factor analysis of variance followed by either a simple t test or a Bonferroni t test for multiple comparisons.


RESULTS
Fentanyl administration did not result in significant changes in duodenal or colorectal distention threshold. Thermal threshold showed an increased trend at the 15-minute time point for the highest fentanyl group only, with a corresponding mean serum fentanyl concentration of 7.82 +/- 2.10 ng/mL. Two horses in this group became agitated and tachycardic during the first 15 minutes of the infusion.


CONCLUSIONS
Fentanyl did not produce a significant antinociceptive effect at the doses used, 2 of which resulted in serum concentrations above the nociceptive threshold in other species.
Sanchez
L Chris
LC
Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA. sanchezl@mail.vetmed.ufl.edu
Robertson
Sheilah A
SA
Maxwell
Lara K
LK
Zientek
Keith
K
Cole
Cynthia
C
D000701:Analgesics, Opioid / Q000493:pharmacokinetics / Q000494:pharmacology*; D000704:Analysis of Variance; D000818:Animals; D001831:Body Temperature / Q000187:drug effects; D003106:Colon / Q000187:drug effects; D005260:Female; D005283:Fentanyl / Q000493:pharmacokinetics / Q000494:pharmacology*; D005769:Gastrointestinal Motility / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D006736:Horses / Q000378:metabolism / Q000502:physiology*; D007275:Injections, Intravenous / Q000662:veterinary; D008297:Male; D010147:Pain Measurement / Q000187:drug effects* / Q000662:veterinary*; D011897:Random Allocation; D012119:Respiration / Q000187:drug effects; D013270:Stomach / Q000187:drug effects
D000701:Analgesics, Opioid; D005283:Fentanyl