The use of fentanyl-patch in dogs undergoing spinal surgery: plasma concentration and analgesic efficacy

Objectives of this study were to evaluate plasma concentrations and analgesic efficacy of fentanyl administered transdermically in dogs undergoing spinal surgery. At the end of the surgery and before awakening, a fentanyl-patch was applied and was maintained in situ for 72 h. Blood samples were taken before the application of the patch, at 2, 4, 6, 8, 10, 12, 18, 24, 32, 40, 48, 60, and 72 h after application and then 2, 4, 6, 8, 10, and 12 h after its removal. Before each blood sampling, pain evaluation was carried out using the Glasgow pain score, appropriately modified. Plasma concentrations of fentanyl were determined using a specific immuno-enzymatic kit. In this study, the minimum analgesic plasma concentration (0.23 ng/mL) required to achieve analgesia in human and considered to apply also for dogs was reached in all animals. No animal showed pain in the range of 'intense pain'; in two cases, the level of the pain was slight or moderate. No undesired effects were found. Results suggest that the use of transdermic patches could represent a valid aid in pain therapy in small animals; in particular, it contributes to the postoperative well-being of patients undergoing major surgery.