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Conference abstract, 2016

Pain assessment in the horse: effect of methadone alone and methadone in combination with detomidine in horses

Olsén, Lena; Ingvast Larsson, Carina


Background: In pain management it is important to assess pain and pain relief in a robust way. Thermal threshold are experimentally used in pain assessment for several species including horses. Opioids such as methadone are effective in treatment of nociceptive pain but may also cause effects on traits used for assessing pain such as cortisol levels. Also alpha2-adrenoceptor agonists (α2-agonists) such as detomidine are commonly used for analgesia and sedation both separately and in combination with opioids. The possible influence of detomidine of the effects of methadone is not well studied in horses. Objectives: The aims of this study were to reveal possible drug effects on pain assessment tools and to optimize pain treatment in horses. The effects on plasma cortisol levels was examined and the analgesic effect was measured with a thermal threshold testing system adopted for horses was used after treatment with methadone IV or methadone IV in combination with detomidine IM. Materials and methods: The study was a randomized blinded placebo controlled with cross over design. Eight Standardbred horses were treated with (1) methadone IV (0.2 mg/kg) in a total volume of 20 mL over 5 min together with placebo (saline) IM or (2) 20 mL methadone IV (0.1 mg/kg) over 5 min together with detomidine IM (0.01 mg/kg) or (3) equivalent volumes placebo (saline) IV and IM. The cortisol levels and analgesia after administration of methadone alone and together with detomidine were examined. Blood samples were collected and the plasma concentrations of cortisol were quantified with a commercial cortisol ELISA kit validated in horses. Results: After both administration of methadone and the combination methadone/detomidine a rise in the plasma cortisol concentration compared to control (P < 0.05) occurred. The thermal threshold was elevated and analgesia was apparent for 1 h when treated with methadone compared to saline (P = 0.001) and for up to 2 h when combining methadone and detomidine (P = 0.02). Conclusions: Both methadone and the combination methadone/ detomidine induced the release of plasma cortisol in horses per se. Plasma cortisol concentration is not a useful tool to assess stress or pain in horses treated with methadone. The duration of the analgesic effect of methadone were short but when combined with detomidine the duration was prolonged. For extended analgesia a constant rate infusion of methadone could be used. Acknowledgements: Supported by The Swedish-Norwegian Foundation for Equine Research.

Published in

Acta Veterinaria Scandinavica
2016, Volume: 58, number: Suppl2


9th international symposium on veterinary rehabilitation and physical therapy, 2016-08-08--2016-08-12, Uppsala, Sweden