Alfaxalone is a steroid hypnotic agent with a wide margin of safety. Its use in dogs is limited by its formulation that incorporates Cremaphor EL which causes histamine release. Cyclodextrin (CD) has been tried as a vehicle for alfaxalone. This study compared the alfaxalone/CD formulation and propofol as induction agents in dogs. Six mature healthy mixed breed dogs with weights ranging from 19.4 to 34.5 kg were used. Acepromazine was administered subcutaneously at 0.2 mg/kg, 30 minutes before administration of either induction agent. Heart rate (HR), respiratory rate (RR), and systemic blood pressure (BP) were monitored immediately before administration of the induction agent and at specified time intervals after induction. Either alfaxalone/CD or propofol were administered IV at 1.2 mg/kg and 3.0 mg/kg, respectively over 1 minute. The dogs received each agent at different times at least 2 weeks apart. Quality of induction and recovery were graded. End-tidal CO2 tension (PETCO2) was monitored after induction and until recovery. Changes in cardiopulmonary variables were analyzed by one-way analysis of variance for repeated measures. Induction and recovery scores and times measured were compared using the Mann-Whitney test. Values are expressed in mean ± SD. Differences were considered significant when P < 0.05. All dogs had excellent anesthetic induction and recovery. There were no signs of pain during injection. None of the dogs showed signs of anaphylactoid reaction to the induction agents. Dogs given alfaxalone and propofol became unconscious at 40.7 ± 6.5 and 48.2 ± 14.3 seconds after the start of drug administration, respectively. Tracheal intubation was successful in all dogs given alfaxalone/CD and in 5 of 6 dogs given propofol. All dogs exhibited light plane of anesthesia characterized by active palpebral reflex. The dogs were standing at 44.7 ± 19.3 and 50.0 ± 13.6 minutes after alfaxalone and propofol induction, respectively. There were no significant differences in HR and RR between alfaxalone/CD and propofol at specific time intervals. The BP of the two groups were similar. Neither propofol nor alfaxalone/CD produced significant reduction in BP. The PETCO2 of the alfaxalone/CD group (25.7 ± 10.2 mmHg) was significantly lower than that of the propofol group (30.5 ± 7.0 mmHg). In conclusion, induction of anesthesia using alfaxalone/CD in premedicated dogs compared favorably with propofol. Further studies are needed to document the safety and efficacy of alfaxalone/CD as an anesthetic agent in dogs.
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