Investigation of Nociceptive Pathway Modulation by Multimodal Analgesia Protocols in Canine Post-Surgical Pain: A Neurochemical and Behavioral Study in Nigeria

Inadequate postoperative pain management results in maladaptive neuroplastic changes, prolonged recovery, and reduced patient welfare in dogs following major surgery. The neurochemical basis of nociceptive pathway modulation by multimodal analgesia protocols has not been investigated in the Nigerian veterinary patient population, where analgesic practices remain inconsistent. This doctoral study investigates the neurochemical and behavioral effects of a multimodal analgesia protocol combining meloxicam, tramadol, and lidocaine constant rate infusion on nociceptive pathway biomarkers in dogs undergoing major orthopedic surgery at three teaching hospitals in Lagos, Abuja, and Ibadan between 2022 and 2024. Sixty dogs were randomized to multimodal analgesia or conventional single-agent NSAID-only analgesia. Serum substance P, beta-endorphin, cortisol, and glucose were measured at baseline and at two, eight, and 24 hours postoperatively as neurochemical indicators of nociceptive activation. Behavioral pain scores were assessed using the Glasgow Composite Measure Pain Scale. Dogs receiving multimodal analgesia demonstrated significantly lower postoperative serum substance P levels at two and eight hours compared to controls, indicating attenuated central sensitization. Beta-endorphin levels were lower in the multimodal group, consistent with reduced endogenous pain response activation. Behavioral pain scores were significantly lower at all postoperative time points in the multimodal group. Rescue analgesia requirements were reduced by 58% in the multimodal protocol group. This study provides the first neurochemical evidence base for multimodal analgesia superiority in canine post-surgical pain management in Nigeria, offering foundational data to support evidence-based analgesic guideline development. Keywords: multimodal analgesia, nociception, canine pain, neurochemistry, postoperative pain.