Comparison of the Transdermal and Intravenous Administration of Buprenorphine in the Management of Intra- and Postoperative Pain in Dogs Undergoing a Unilateral Mastectomy

SIMPLE SUMMARY: A mastectomy is the gold standard of treatment for mammary tumors in dogs; nevertheless, surgical stimuli cause extensive inflammation and moderate–severe perioperative pain. Opioids are the most widely used drugs in both human and veterinary medicine for the management of pain; however, their systemic administration is not free from side effects (nausea, vomiting, dysphoria, and cardiac and respiratory depression). The administration of analgesics through a transdermal route offers an interesting alternative for the maintenance of a stable and prolonged plasma concentration of the drug, therefore avoiding most of the drawbacks of their parenteral administration. The aim of this clinical study was to evaluate the intraoperative and postoperative analgesic efficacy of buprenorphine administered through transdermal patches compared to the intravenous route in dogs undergoing a monolateral mastectomy. The results of this study showed that the transdermal administration of buprenorphine could guarantee an analgesic quality equal to the injectable route. Furthermore, it must be considered that it would guarantee the continuous administration of an opioid while avoiding repeated injections (especially in fearful or aggressive dogs). ABSTRACT: The aim of this prospective clinical study was to evaluate the effectiveness of transdermal patches of buprenorphine as an alternative route for the management of perioperative pain in dogs undergoing a unilateral mastectomy. Our hypothesis was that the transdermal route would allow the obtainment of an analgesic plan comparable to that of the injectable administration. Twelve dogs were divided in two groups. In the BupreP group (six dogs), buprenorphine patches were applied 40 h before the start of the surgery, guaranteeing a dosage of 5–6 μg/kg/h. In the BupreI group (six dogs), 20 μg/kg of buprenorphine was administered intravenously 30 min before the induction of anesthesia, and this was repeated every 6 h for 24 h. The main physiological parameters, sedation scores (0 = no sedation; 11 = deep sedation), and pain scores were monitored from 30 min before the surgery to 24 h after the end of anesthesia. All p values < 0.05 were defined as statistically significant. Thirty minutes before the surgery, the sedation scores were higher in BupreI (score = 10) compared to the BupreP group (score = 1). Moreover, during the mastectomy, the mean arterial pressure significantly increased in both groups even if nobody required additional analgesia. In the postoperative period, the pain scores did not show statistically significant differences between the two groups, maintaining values below the pain threshold at all times of the study. In conclusion, the transdermal administration of buprenorphine could guarantee an analgesic quality equal to that of the injectable route.