Subcutaneous methadone is not different than transdermal fentanyl for postoperative analgesia in dogs with thoracolumbar disc disease, using three different pain scales and von Frey Filaments, a prospective, randomised, blinded clinical study

Background Thoracolumbar disc disease is a common neurological disease in dogs, which incorporated different pain components. Multimodal analgesic treatments especially postoperatively, are often based on opiods and require an intravenous catheter for drug application. This might impede early mobilisation and physiotherapy. Different composite pain scales and sensory testing devices exist to evaluate postoperative pain behaviour in dogs. At present, no data are available to clearly recommend one tool or technique after spinal surgery over others. Therefore, the primary aim of this study was to evaluate if, subcutaneously applied methadone or transdermal fentanyl can offer sufficient postoperative analgesia in dogs after thoracolumbar neurosurgery without the necessity of keeping an intravenous access. A secondary aim was to evaluate which type of pain recognition tool would be suitable in this dogs in a clinical setting. Methods In a prospective, randomised, clinical study client fifty client owned dogs were repeatable evaluated for 96h post spinal surgery. Treatments groups M received 0.4 mg/kg methadone subcutaneously two hours before start of surgery and following this every 6 hours. Treatment group F received topical applied 2.6 mg/ kg transdermal – fentanyl, two hours before start of the surgery. Dogs were assessed using the Glasgow composite measure pain scale – short form (CMPS-SF), the Colorado State University canine acute pain scale (CPS), a visual analogue scale and von Frey Monofilaments. Treatments groups were compared using the Wilcoxen rang sum test. Correlation between the three pain score was evaluated using the Spearman Rang correlation coefficient. Results At no time point, any of the used methods could demonstrate a significant difference between analgesic requirements between groups M and F (p < 0.05). In both treatment groups pain scores of all three scales decreased over time. Results of the different pain scales correlated moderately to strongly. Utilising von Frey Filaments, results for skin sensitivity showed large individual variation, with a tendency towards reaction only at thicker filaments. Conclusion Subcutaneously methadone or transdermal fentanyl can provide adequate postoperative analgesia in dogs after spinal surgery without an intravenous catheter. The CMPS-SF and the CPS could reliably be used in this category of animal.