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Ketamine, a noncompetitive NMDA receptor antagonist, has been shown to provide analgesia in some species. To target the NMDA receptor specifically and to potentially minimize some untoward side-effects, ketamine had been used epidurally. The objective of this study was to determine the analgesic effect of epidurally administered ketamine in dogs with chemically induced synovitis. Sixteen healthy dogs were used. Dogs were anesthetized with propofol (4 mg kg−1 IV). Synovitis was induced by injecting 1 mL of sodium urate crystal solution (10 mg mL−1) into the right stifle. Dogs were allowed to recover and the synovitis was allowed to develop for 12 hours. The dogs were then anesthetized again using propofol (4 mg kg−1 IV). Lumbosacral epidural injections were performed with each dog receiving either 2 mg kg−1 of ketamine (20 mg mL−1) or an equal volume of placebo (sterile water containing not more than 0.1 mg mL−1 benzethonium chloride). Analgesia was assessed at baseline and then at 12, 14, 16, 18, 20, and 24 hours after induction of synovitis. Ground reaction forces (peak vertical force and impulse area) and overall pain were measured using a force platform and a pain scoring system (numerical rating scale). Analysis of the data by Repeated Measures anova showed that the dogs developed a significant lameness between the baseline and 12 hours. However, no significant difference in ground reaction forces or total pain score was demonstrated between the treatment and control groups at any other time. In conclusion, ketamine administered epidurally at a dose of 2 mg kg−1 did not provide significant analgesia in dogs with chemically induced synovitis.

Objective To determine if epidural ketamine provides analgesia in dogs with a chemically induced synovitis. Study design Prospective randomized experimental trial. Animals Thirty-two healthy, adult mongrel dogs (13–30 kg). Methods (Part I) Synovitis was induced in the right stifle of 16 dogs and allowed to develop for 12 hours. Epidural injection at the lumbosacral space of either ketamine (2 mg kg −1 ; n = 8) or placebo ( n = 8) was performed. Limb use and pain were measured using a force platform and numerical rating scale (NRS). Assessments were performed before and at 12, 14, 16, 18, 20, and 24 hours after the induction of synovitis. (Part II) Epidural injection of either ketamine ( n = 8) or placebo ( n = 8) was performed immediately before the induction of synovitis. Analgesia was assessed as in Part I. Assessments occurred before and at 2, 4, 6, 8, and 12 hours after the induction of synovitis. Results (Part I) Vertical ground reaction forces (VGRF) significantly decreased and NRS scores of total pain significantly increased after the induction of synovitis in all dogs ( p 0.05). No significant differences in VGRF or NRS scores were measured between treatment groups at any assessment period. (Part II) Dogs that received ketamine had significantly lower NRS scores 2 hours after treatment ( p 0.05). NRS scores did not differ between groups at any other evaluation. VGRF did not differ significantly between treatment groups at any assessment period. Conclusion Epidural ketamine at a dose of 2 mg kg −1 administered after the development of synovitis does not provide significant levels of analgesia. Administration of ketamine before the induction of synovitis significantly decreased the NRS score 2 hours post-induction. Clinical relevance Administration of epidural ketamine before tissue injury may provide analgesia of short duration in dogs.