Plasma concentrations of transdermal fentanyl and buprenorphine in pigs (Sus scrofa domesticus).

ABSTRACT

OBJECTIVE: To determine the absorption characteristics of fentanyl and buprenorphine administered transdermally in swine. STUDY DESIGN: A randomized comparative experimental trial. ANIMALS Twenty-four Yorkshire gilts weighing 27.8±2.2 kg (mean±standard deviation). METHODS: Animals were randomly assigned to different doses of transdermal patches (TPs) of fentanyl (50 µg hour-1, 75 µg hour-1 and 100 µg hour-1) or buprenorphine (35 µg hour-1 and 70 µg hour-1), once or twice. Thirteen blood samples were obtained for each TP applied. Plasma concentrations were determined, and the area under the curve, peak serum concentration (Cmax) and time to Cmax were calculated. RESULTS: Fentanyl Cmax was observed at different time points for the first TP application 30 hours for 50 µg hour-1, 6 hours for 75 µg hour-1 and 100 µg hour-1 patches; and for the second TP application 30 hours for 50 µg hour-1 and 36 hours for 75 µg hour-1 patches. Buprenorphine serum concentrations were not detected for the 35 µg hour-1 patch; Cmax was observed at different times for the 70 µg hour-1 patch 18 hours (n = 1), 24 hours (n = 3), 30 hours (n = 1) and 42 hours (n = 1) after application of the first patch and 12 hours after the second patch. CONCLUSIONS AND CLINICAL RELEVANCE A relevant serum concentration obtained with fentanyl TP dosed at 75 µg hour-1 or 100 µg hour-1suggests that TPs could represent an analgesia option for laboratory pigs weighing 25-30 kg. As concentrations of buprenorphine were variable, this study does not support the use of buprenorphine TPs in pigs. Consecutive fentanyl or buprenorphine TPs did not provide reliable serum concentrations. Further pharmacokinetic studies and analgesiometric tests in swine are needed to confirm the clinical adequacy of TPs.