A study to evaluate buprenorphine at 40 μg kg(-1) compared to 20 μg kg(-1) as a post-operative analgesic in the dog.

Objective: Comparison of the analgesic effect of buprenorphine at 20 or 40 μg kg(-1) .

Study Design: An investigator 'blinded', randomised study.

Animals: Twenty six dogs presented for ovariohysterectomy.

Methods: Dogs were premedicated intramuscularly with acepromazine 0.03 mg kg(-1) and buprenorphine at either 20 (B20, n = 12) or 40 μg kg(-1) (B40, n = 14) followed by anaesthetic induction with propofol and maintenance with isoflurane. During anaesthesia non invasive blood pressure, heart rate, respiratory rate, blood oxygen saturation, inspired and expired volatile agent, end-tidal carbon dioxide and ECG were recorded. Pain and sedation were assessed using interactive VAS scores; mechanical nociceptive thresholds were measured at the wound and hindlimb--all were assessed before and up to 22 hours after administration. Carprofen was used for rescue analgesia.

Results: There were no significant differences between the two groups for any of the parameters examined. Rescue analgesia was required around 5 hours after administration of buprenorphine in a significant number of animals. Sedation was good preoperatively and scores decreased over time postoperatively. Hock thresholds did not change over time; wound thresholds decreased significantly compared to the baseline value from 3 hours onwards.

Conclusions: Administration of buprenorphine at either 20 or 40 μg kg(-1) IM with acepromazine provided good pre-operative sedation. Cardiovascular and respiratory values remained within clinically acceptable limits during anaesthesia. There was no evidence that increasing dose increased adverse events that may be associated with opioid administration (e.g. bradycardia and respiratory depression).

Clinical Relevance: Increasing the dose of buprenorphine from 20 to 40 μg kg(-1) did not provide any benefits with respect to analgesia after ovariohysterectomy as assessed using the VAS scoring system.