• Eduardo Raposo Monteiro, Adolfo Rodrigues Junior, Hemir Martins Quirilos Assis, Daniela Campagnol, and Juliany Gomes Quitzan.
• Faculty of Veterinary Medicine, Centro Universitário de Maringá (CESUMAR), Paraná, Brazil. btraposo@hotmail.com
• Vet Anaesth Analg. 2009 Jan 1;36(1):25-33.

ObjectiveTo compare the effects of morphine (MOR), methadone (MET), butorphanol (BUT) and tramadol (TRA), in combination with acepromazine, on sedation, cardiorespiratory variables, body temperature and incidence of emesis in dogs.Study DesignProspective randomized, blinded, experimental trial.AnimalsSix adult mixed-breed male dogs weighing 12.0 +/- 4.3 kg.MethodsDogs received intravenous administration (IV) of acepromazine (0.05 mg kg(-1)) and 15 minutes later, one of four opioids was randomly administered IV in a cross-over design, with at least 1-week intervals. Dogs then received MOR 0.5 mg kg(-1); MET 0.5 mg kg(-1); BUT 0.15 mg kg(-1); or TRA 2.0 mg kg(-1). Indirect systolic arterial pressure (SAP), heart rate (HR), respiratory rate (f(R)), rectal temperature, pedal withdrawal reflex and sedation were evaluated at regular intervals for 90 minutes.ResultsAcepromazine administration decreased SAP, HR and temperature and produced mild sedation. All opioids further decreased temperature and MOR, BUT and TRA were associated with further decreases in HR. Tramadol decreased SAP whereas BUT decreased f(R) compared with values before opioid administration. Retching was observed in five of six dogs and vomiting occurred in one dog in MOR, but not in any dog in the remaining treatments. Sedation scores were greater in MET followed by MOR and BUT. Tramadol was associated with minor changes in sedation produced by acepromazine alone.Conclusions And Clinical RelevanceWhen used with acepromazine, MET appears to provide better sedation than MOR, BUT and TRA. If vomiting is to be avoided, MET, BUT and TRA may be better options than MOR.

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