The analgesic effects of three different doses of tramadol as a preanesthetic in medetomidine-ketamine anesthesia in dogs were compared. Twenty-eight healthy adult mongrel dogs were used. The dogs were divided into four groups at random; 1 ml/kg of normal saline, 1, 2 or 4mg kg^-1 of tramadol premedication (group Control, TRA1, TRA2 and TRA4) was then administered intravenously followed by medetomidine and ketamine anesthesia. The behavioral changes, the duration of surgical anesthesia, blood gas parameters (pH, pO₂, and pCO₂), heart rate, and systolic/diastolic pressure were observed. Tramadol (4mg kg^-1) pretreatment significantly increased the degree of sedation when compared with the control, TRA1 and TRA2 groups at 15 min after tramadol administration (P<0.05). The duration of surgical anesthesia was significantly increased by tramadol (4mg kg^-1) pretreatment when compared with that of the control group (P<0.05). There were no significant differences in behavioral changes, blood gas parameters (pH, pO2 and pCO2), heart rate, and arterial pressure among the groups. Tramadol at 4mg kg^-1 did not affect the cardiovascular system and recovery of anesthesia, but significantly increased the duration of surgical anesthesia with medetomidine and ketamine. This result suggests that intravenous tramadol at 4mg kg^-1 is a useful preanesthetic agent for extending the surgical level of anesthesia in medetomidine-ketamine anesthesia in dogs.

Key words: Dog; Duration of surgical anesthesia; Ketamine; Medetomidine; Tramadol