Analgesic Efficacy and Hematobiochemical Profiles of Tramadol, Lidocaine, and Their Combination Following Brachial Plexus Blockade in Rabbits

Abstract

Background: Effective perioperative pain management remains a critical challenge in lagomorph medicine because rabbits have high physiological stress reactivity and sensitivity to general anaesthetics. Landmark-guided brachial plexus blockade offers targeted regional analgesia for forelimb procedures. Amide local anaesthetics such as lidocaine provide rapid desensitization but have a short therapeutic window, whereas atypical opioids such as tramadol provide extended antinociception but have a delayed onset. Objective of the Study: This study evaluated the analgesic efficacy, onset time, and total block duration of tramadol, lidocaine, and their combination via brachial plexus blockade in rabbits, together with their sequential haematobiochemical effects. Materials and Methods: Nine healthy adult rabbits were randomised into three parallel cohorts (n = 3/group) to receive perineural injections of 5% tramadol (3 mg/kg), 2% lidocaine (7 mg/kg), or a combined tramadol-lidocaine mixture (1.5 mg/kg and 3.5 mg/kg) into the axillary space. Antinociception was verified using mechanical forceps clamping and pin-prick stimulation. Serial blood samples were collected from the marginal ear vein between 0 and 100 minutes post-injection to determine haematological variables and serum biochemical profiles using a semi-automated chemistry analyser. Results: Analgesic onset was significantly faster in the lidocaine (3.0 ± 0.71 min) and combination groups (4.0 ± 0.0 min) than with tramadol alone (12.0 ± 4.95 min; P < 0.05). Total analgesic duration was significantly extended by tramadol alone (52.0 ± 2.83 min) and the combination (45.0 ± 4.24 min) compared with lidocaine alone (36.0 ± 2.02 min; P < 0.05). Lidocaine alone induced progressive haemodilution by 80 minutes (P < 0.05), while tramadol alone triggered a sharp leukocyte spike (P < 0.01). Co-administration balanced these shifts and maintained stable haematological and serum biochemical profiles. Conclusion: The perineural tramadol-lidocaine combination provided rapid and prolonged regional analgesia for rabbit forelimb procedures lasting up to 60 minutes, with acceptable transient haematobiochemical variations.