Plasma Concentrations of Fentanyl Achieved With Transdermal Application in Chickens

Providing appropriate analgesia is an important concern in any species. Fentanyl, a μ-receptor specific opioid, use is common in mammalian species but has been incompletely evaluated for this purpose in avian species. Transdermal fentanyl patches were applied to domestic chickens (n = 10) of varying breeds for 72 hours. Repeated blood samples were collected from the birds to assess time-concentration of fentanyl and norfentanyl in plasma, as assayed by liquid chromatography-mass spectrometry, throughout patch application and for 48 hours after patch removal. Compartmental modeling was used to characterize the elimination profiles. Evaluation as a large bolus, followed by slower elimination rates over the remaining time, best fit the data as a one-compartment open model. Although maximum plasma fentanyl concentrations varied substantially by individual birds, chickens trended into 2 general groups of maximum plasma concentration, clearance, and volume of distribution, which was attributed to absorption variability. For all birds, harmonic mean of elimination half-life was 7.2 ± 3.7 hours and showed less individual variation than the other pharmacokinetic parameters. Because the application of transdermal fentanyl patches in the chickens achieved plasma fentanyl concentrations considered therapeutic in people, this approach could provide an additional analgesic option for avian patients.