PURPOSE: To compare the postoperative analgesic effects of lidocaine, morphine and lidocaine plus morphine administered by constant rate infusion (CRI) and analyzing their effects on opioid requirements after orthopedic surgery in dogs.METHODS: Twenty-four dogs underwent fracture repairs were premedicated with IM acepromazine (0.05 mg/kg) combined with morphine (0.3mg/kg). Anesthesia was induced with IV propofol (4 to 5 mg/ kg) and maintained with isoflurane. The dogs were randomly assigned to 3 groups and administered a CRI IV of lidocaine (T-L), morphine (T-M) or lidocaine plus morphine (T-LM) at the same doses. Postoperative analgesia was assessed for 24 hours using a Visual Analog Scale (VAS) and the Glasgow Composite Pain Scale (GCPS). Rescue analgesia was performed if the evaluation score exceeded 50% of the VAS and/or 33% of the GCPS.RESULTS: The pain score and postoperative opioid requirements did not differ among the treatments. Rescue analgesia was administered to 1/8 dogs in the T-M and T-LM, and to 3/8 dogs in the T-L.CONCLUSION: Lidocaine, morphine or lidocaine/morphine CRI may be efficacious techniques for pain management in the first 24 hours post-surgery. However, the two drugs administered together did not reduce the postoperative opioid requirement in dogs undergoing fracture repair. Key words: Anesthesia. Analgesics. Analgesics, Opioid. Lidocaine. Morphine. Dogs.