Evaluation of the analgesic effects of epidurally administered morphine, alfentanil, butorphanol, tramadol, and U50488H in horses.
OBJECTIVE
To evaluate and compare effects of epidurally administered morphine, alfentanil, butorphanol, tramadol, and U50488H on avoidance threshold to noxious electrical stimulation over the dermatomes of the perineal, sacral, lumbar, and thoracic regions in horses.


METHODS
5 healthy adult horses.


METHODS
Using a Latin square complete repeated-measures design, horses were randomly assigned to receive 1 of 6 treatments (morphine, alfentanil, butorphanol, tramadol, U50488H, or sterile water) at intervals of at least 7 days. Agents were injected epidurally at the first intercoccygeal epidural space, and electrical stimulation was applied at repeated intervals for 24 hours to the dermatomes of the perineal, sacral, lumbar, and thoracic regions. Avoidance threshold to electrical stimulation was recorded.


RESULTS
Administration of butorphanol, U50488H, and sterile water did not induce change in avoidance threshold. Alfentanil increased avoidance threshold during the first 4 hours, but not significantly. Tramadol and morphine significantly increased threshold and analgesic effects. Complete analgesia (avoidance threshold, >40 V) in the perineal and sacral areas was achieved 30 minutes after tramadol injection, compared with 6 hours after morphine injection. Duration of complete analgesia was 4 hours and 5 hours after tramadol and morphine injections, respectively.


CONCLUSIONS
Epidural administration of tramadol and morphine induces long-lasting analgesia in healthy adult horses. Epidural administration of opioids may provide long-lasting analgesia in horses without excitation of the CNS.
Natalini
C C
CC
Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Minnesota, St Paul 55108, USA.
Robinson
E P
EP
D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer / Q000494:pharmacology*; D015760:Alfentanil / Q000008:administration & dosage / Q000494:pharmacology*; D015360:Analgesia, Epidural / Q000662:veterinary*; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects; D002077:Butorphanol / Q000008:administration & dosage / Q000494:pharmacology*; D004558:Electric Stimulation; D006736:Horses; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D010146:Pain / Q000503:physiopathology; D017288:Pain Threshold / Q000187:drug effects; D014147:Tramadol / Q000008:administration & dosage / Q000494:pharmacology*
D015760:Alfentanil; D014147:Tramadol; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D009020:Morphine; D002077:Butorphanol