RESEARCH PAPER Comparison of analgesia provided by lidocaine, lidocaine–morphine or lidocaine–tramadol delivered epidurally in dogs following orchiectomy Ricardo M Almeida*, Andre ´ Escobar & Samara Maguilnik* *School of Agriculture and Veterinary Medicine, Universidade de Brası ´lia, Brası ´lia, DF, Brazil  Department of Veterinary Clinics and Surgery, Universidade Estadual Paulista, Jaboticabal, SP, Brazil Correspondence: Ricardo Miyasaka de Almeida, Hospital Escola de Grandes Animais da UnB, Galpa ˜o 04, Granja do Torto, CEP 70636-200, Brası ´lia, DF, Brazil. E-mail: ricardoalmeida@unb.br Abstract Objective To evaluate and compare the postopera- tive analgesia provided by epidural lidocaine, lido- caine/morphine or lidocaine/tramadol in dogs following elective orchiectomy. Study design Prospective experimental trial. Animals Thirty-six mongrel dogs aged 2–8 years old, weighing 6.6–22 kg. Methods The dogs received 6.0 mg kg )1 of lido- caine combined with 1.0 mg kg )1 of tramadol, 0.1 mg kg )1 of morphine or 0.01 mL kg )1 of 0.9% NaCl epidurally. Analgesia was assessed at 4, 8, 12, 18 and 24 hours (T4, T8, T12 and T24) after the offset of lidocaine using a scale composed of physiologic and behavioral parameters. Rescue analgesia with morphine (0.2 mg kg )1 , IM) was performed if the evaluation score exceeded 10 during the postoperative period. The scores over time were analyzed using the Friedman’s two-way analysis of variance and the comparison between groups was made by the Kruskal–Wallis test with statistical significances accepted if p £ 0.05. Results There were no differences in the pain scores between the morphine and tramadol groups over time and no rescue analgesia was administered. In the NaCl group, rescue analgesia was needed at T4, T8 and T12. Within this group, the final evaluation times (T18 and T24) had lower pain scores than at T4, T8 and T12. Conclusions and clinical relevance Epidural lido- caine/tramadol provided an analgesic effect compa- rable to that of epidural lidocaine/morphine during the first 12 hours after surgical castration without substantial side effects, suggesting that tramadol may be an effective postoperative analgesic in dogs submitted to this surgical procedure. Keywords analgesia, dog, epidural, morphine, orchi- ectomy, tramadol. Introduction Postoperative analgesia is of utmost importance because pain causes various deleterious effects that hinder the recovery of the patient (Hansen 2005). Among these harmful effects are negative protein balance, decreased food intake, release of stress hormones, possibility of self-mutilation, weight loss, delayed healing of a surgical wound, immunosup- pression, and increase in arterial blood pressure (Gwendolyn & Carrol 1996; Gaynor 1999). Opioids are used perioperatively for the manage- ment of pain, but because of their relatively short half-life, they may need to be administered multiple times, which increases the incidence of side effects. When injected epidurally, they bind to specific 542 Veterinary Anaesthesia and Analgesia, 2010, 37, 542–549 doi:10.1111/j.1467-2995.2010.00563.x