Evaluation of the analgesic and pharmacokinetic properties of transdermally administered fentanyl in goats.

OBJECTIVE: Evaluate the analgesic properties and pharmacokinetics of transdermal fentanyl patches (TFPs) in goats. DESIGN: Prospective, randomized study. SETTING: Preclinical Testing Facility at a University Teaching Hospital. ANIMALS: Thirty-four adult female Boer-cross goats. INTERVENTIONS: Goats underwent surgery as part of a concurrent orthopedic research study. Twelve hours prior to surgery, each goat received a TFP (target dosage of 2.5 µg/kg/h), or a placebo patch with analgesia provided by buprenorphine (0.01 mg/kg, IM, q 6 h). Patches were removed after 72 hours. Blood was sampled at specified intervals, up to 84 hours following TFP placement. Plasma concentrations of fentanyl (FEN) were determined using liquid chromatography-mass spectrometry. Postoperative pain assessments were performed by two independent blinded observers. MEASUREMENTS AND MAIN RESULTS: TFPs were applied at a mean (± standard deviation, SD) dose of 2.54 ± 0.36 µg/kg/h. No adverse events occurred. Pain scores between TFP and BUP groups were not significantly different at any time point. Mean plasma FEN concentration (± SD) 2 hours following patch application was 1.06 ± 0.85 ng/mL, and remained above 0.5 ng/mL for 40 hours. Maximum mean plasma FEN concentration (Cmax ) was 1.84 (ranging from 0.81 to 3.35) ng/mL with average time to maximum concentration (Tmax ) of 12 hours after patch application. CONCLUSIONS: TFP resulted in consistent FEN absorption and plasma concentrations within the human and ovine therapeutic ranges. Pain scores for goats administered TFP were not different than those administered buprenorphine. Ease of administration, duration of analgesia, and decreased dosing frequency make TFPs an attractive option for pain management in goats.

Pharmacokinetics of fentanyl administered transdermally and intravenously in sheep.

OBJECTIVE: To investigate the pharmacokinetics of fentanyl administered transdermally and IV in sheep. ANIMALS: 21 adult female sheep. PROCEDURES: Fentanyl was administered IV to 6 healthy sheep. Transdermal fentanyl patches (TFPs) were applied to 15 sheep 12 hours prior to general anesthesia and surgery. Seria blood samples were collected for 18 hours after IV injection and 84 hours after TFP application. Fentanyl concentrations were quantified via liquid chromatography-mass spectrometry, and pharmacokinetic values were estimated. RESULTS: All sheep completed the study without complications. Following a dose of 2.5 g/kg administered IV, the half-life was 3.08 hours (range, 2.20 to 3.36 hours), volume of distribution at steady state was 8.86 L/kg (range, 5.55 to 15.04 L/kg), and systemic clearance was 3.62 L/kg/h (range, 2.51 to 5.39 L/kg/h). The TFPs were applied at a mean dose of 2.05 g/kg/h. Time to maximum plasma concentration and maximal concentration were 12 hours (range, 4 to 24 hours) and 1.30 ng/mL (range, 0.62 to 2.73 ng/mL), respectively. Fentanyl concentrations were maintained at >0.5 ng/mL for 40 hours after TFP application. CONCLUSIONS AND CLINICAL RELEVANCE: IV administration of fentanyl resulted in a short half-life. Application of a TFP resulted in stable blood fentanyl concentrations in sheep.