Postoperative Analgesic Effects of Epidural Administration of Methadone, Tramadol, or Nalbuphine in Ovariohysterectomized Dogs

The objective of this study was to evaluate the effectiveness of epidural methadone, tramadol or nalbuphine for postoperative analgesia in dogs. Thirty two healthy female dogs (ASA grade 1) undergoing ovariohysterectomy were randomly allocated into 4 treatments of 8 each: treatment 1 (control group) received 2% lidocaine (LD; 4 mg kgG), treatment 2 lidocaine and methadone (LDMT; 4 and 0.3 mg kgG, respectively), treatment 3 lidocaine and tramadol (LDTR; 4 and 2 mg kgG, respectively) and treatment 4 lidocaine and nalbuphine (LDNB; 4 and 0.3 mg kgG, respectively). The drugs were administered into the lumbosacral space, diluted in saline solution to a total volume of 0.36 mL kgG. Heart and respiratory rates, arterial pressures and peripheral SpO2 were evaluated during the peri-operative period until 240 min. Postoperative pain and sedation were measured after extubation until the first rescue analgesic and thereafter regularly for 18 h. The time to first rescue analgesia was significantly (p<0.05) prolonged in dogs in the LDMT group as compared to the control and LDTR or LDNB groups. Although all 3 drug combinations administered epidurally in dogs allowed ovariohysterectomy to be performed with sufficient analgesia, the analgesia was maintained longer with the combination of lidocaine and