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.

Pyrilamine and O-desmethylpyrilamine detection in equine serum and urine.

Pyrilamine (mepyramine) is an H1-receptor antagonist used in human and veterinary medicine. It has the potential to produce central nervous system effects in horses and therefore may have some impact on an outcome of a horse race. A single oral dose of pyrilamine (300 mg/horse) was given to three animals. Serum samples were collected before drug administration and at 0.25, 0.5, 1, 2, 4, 6, 24, 48, 72, 96, 120, and 144 h, and 7, 8, 9, 10, 11, 12, and 13 days post-administration. Urine samples were collected at 0-1, 1-2, 2-4, 4-6, 24, 48, 72, 96, 120, and 144 h, and 7, 8, 9, 10, 11, 12, 13 days post-administration. Urine and serum samples were initially screened by the pyrilamine enzyme-linked immunosorbent assay (ELISA) kit with subsequent confirmation and quantitation utilizing a newly developed and validated gas chromatography-mass spectrometry (GC-MS) method for pyrilamine and its major metabolite O-desmethylpyrilamine with chlorpromazine as an internal standard. Prior to the basic extraction, urine specimens were hydrolyzed using beta-glucuronidase. The urine extracts as well as the serum samples were then subjected to solid-phase extraction on Bond Elut LRC-PRS columns. Pyrilamine was not found in any of the urine samples but it was present in serum in low concentrations (4-123 ng/mL) up to 6 h after drug administration. The limit of detection and limit of quantitation for the GC-MS method for pyrilamine in serum were 1.5 and 3.1 ng/mL, respectively, and for O-desmethylpyrilamine in urine were 5 and 6.2 ng/mL, respectively. Pyrilamine concentration in serum peaked at 15 min, 30 min, and 1 h in horse #1, #2, and #3, respectively. Urine specimens were screened positive for pyrilamine and its metabolites using ELISA for extended periods of time (4 days in one horse and 9 days in two other animals). Using GC-MS, O-desmethylpyrilamine was detected in urine for 11 days in horse #1, 4 days in horse #2, and 9 days in horse #3. While pyrilamine was eliminated from the bloodstream rather quickly, the metabolite level remained in the urine for days after administration. When evaluating laboratory results, regulators must take into account that a urine sample positive for O-desmethylpyrilamine does not necessarily indicate that the drug remains active in the horse's system, possibly affecting the outcome from the race.