Antinociceptive effects of three escalating dexmedetomidine and lignocaine constant rate infusions in conscious horses.
Authors: Risberg A, Spadavecchia C, Ranheim B, Krontveit R, Haga H A
Journal: Veterinary journal (London, England : 1997)
Summary
# Antinociceptive efficacy of dexmedetomidine and lignocaine constant rate infusions in conscious horses When managing pain in standing horses, veterinarians commonly employ intravenous dexmedetomidine and lignocaine, yet their dose-response relationships and plasma concentrations required for analgesia remain incompletely characterised. Risberg and colleagues investigated the analgesic effects of three escalating dexmedetomidine infusion rates (2, 4 and 6 µg/kg/h) and three lignocaine rates (20, 40 and 60 µg/kg/min) in 10 Swiss Warmblood horses by measuring electrically elicited nociceptive withdrawal reflexes via deltoid electromyography, establishing both nociceptive threshold (response to single stimulus) and tolerance (response to repeated stimulation). Dexmedetomidine demonstrated dose-dependent antinociceptive effects at 4 and 6 µg/kg/h but not at 2 µg/kg/h for single stimulation, with a median effective plasma concentration of 0.15 ng/mL (ranging <0.02–0.25 ng/mL); lignocaine required higher plasma concentrations (>600 ng/mL), achievable only at infusion rates of 40 and 60 µg/kg/min, whilst the lowest dose (20 µg/kg/min) provided only modest antinociception to repeated stimulation. The practical significance lies in establishing that 4 µg/kg/h dexmedetomidine and 40 µg/kg/min lignocaine represent the minimum effective rates for consistent analgesia in conscious horses, though substantial inter-individual vari
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Practical Takeaways
- •For conscious horse analgesia, dexmedetomidine at 4 µg/kg/h or lignocaine at 40 µg/kg/min represent effective minimum doses; higher rates provide no additional benefit for dexmedetomidine, while higher lignocaine doses improve threshold but not tolerance
- •Dexmedetomidine produces variable sedation between individual horses at the same dose, requiring clinical observation and potential dose adjustment; lignocaine provides analgesia without sedation, making it suitable for procedures requiring a more alert patient
- •Combined protocols may be considered since lignocaine's analgesic effects are dose-dependent and non-sedating, potentially complementing dexmedetomidine's variable sedative profile for optimal pain management in conscious horses
Key Findings
- •Dexmedetomidine at 4 and 6 µg/kg/h increased nociceptive threshold and tolerance, with median effective plasma concentration of 0.15 ng/mL (range <0.02-0.25 ng/mL)
- •Lignocaine at 40 and 60 µg/kg/min increased both nociceptive threshold and tolerance at plasma concentrations >600 ng/mL, while 20 µg/kg/min only increased tolerance to repeated stimulation
- •Dexmedetomidine at 4 µg/kg/h and lignocaine at 40 µg/kg/min were the lowest infusion rates producing consistent antinociception across all parameters
- •Large individual variability in dexmedetomidine plasma concentrations and sedative effects was observed, whereas lignocaine did not induce significant sedation