Sedative and antinociceptive effects of different detomidine constant rate infusions, with or without methadone in standing horses

Miguel Gozalo Marcilla, A Rodrigues de Oliveira, M Werneck Fonseca, F Sossai Possebon, L Pelligand, P M Taylor, S P Loureiro Luna

Research output: Contribution to journalArticlepeer-review


BACKGROUND: Standing surgery avoids the risks of general anaesthesia in horses.OBJECTIVES: To assess sedation, antinociception and gastrointestinal motility in standing horses after a detomidine loading dose and 2-hours constant rate intravenous (i.v.) infusion, with or without methadone.STUDY DESIGN: Blinded, randomised, crossover with seven healthy adult cross-bred horses, three geldings and four females (404 ± 22 kg).METHODS: Five i.v. treatments were administered to all horses with 1-week washout period: saline (SAL), detomidine low (2.5 μg/kg bwt + 6.25 μg/kg bwt/h) (DL) and high doses (5 μg/kg bwt + 12.5 μg/kg bwt/h) (DH) alone or combined with methadone (0.2 mg/kg bwt + 0.05 mg/kg bwt/h), (DLM) and (DHM), respectively. Height of head above the ground (HHAG), electrical (ET), thermal (TT) and mechanical (MT) nociceptive thresholds and gastrointestinal motility were evaluated at predetermined times between 5 and 240 minutes. A mixed effect model and Kruskal-Wallis test were used to analyse normally and non-normally distributed data, respectively.

RESULTS: Sedation (<50% basal HHAG) was achieved for the duration of the infusion, and for an additional 15 minutes in DH and DHM groups. Nociceptive thresholds were higher than baseline, to the greatest degree and the longest duration, with DHM (ET and TT for 135 minutes and MT for 150 minutes). After DH, TT was significantly higher than baseline from 30 to 120 minutes and MT from 15 to 135 minutes. After DLM, ET was increased at 90 minutes, TT at 30 minutes and MT for 120 minutes. Gastrointestinal motility was reduced for up to 135 minutes after DL, 150 minutes after DLM and 210 minutes after DH and DHM.

MAIN LIMITATIONS: Nociceptive thresholds are not equivalent to surgical stimuli.

CONCLUSION: Methadone with the highest detomidine dose (DHM) may provide sufficient sedation and analgesia for standing surgical procedures and warrants further investigation. This article is protected by copyright. All rights reserved.

Original languageEnglish
JournalEquine Veterinary Journal
Early online date28 Nov 2018
Publication statusE-pub ahead of print - 28 Nov 2018


  • horse
  • detomidine
  • methadone
  • constant rate infusion
  • electrical stimulus
  • thermal stimulus
  • mechanical stimulus


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