Pharmacokinetics of fentanyl after intravenous and transdermal administration in goats.
OBJECTIVE
To evaluate disposition of fentanyl in goats after IV and transdermal administration.


METHODS
8 healthy 2-year-old goats weighing 31.8 to 53.6 kg (mean+/-SD, 40.4+/-7.5 kg).


METHODS
Each goat was given 2 treatments consisting of fentanyl administered IV (2.5 microg/kg of body weight) and via a transdermal patch (50 microg/h). There was a 2-month interval between treatments. Blood samples were collected at specified times and analyzed in duplicate to determine plasma fentanyl concentrations. Pharmacokinetic values were calculated, using a computerized modeling program.


RESULTS
Administration of fentanyl was tolerated by all goats. Intravenous administration of fentanyl resulted in a transitory increase in rectal temperature that was not clinically important. Terminal elimination half-life after IV administration was 1.20+/-0.78 h, volume of distribution at steady state was 1.51+/-0.39 L/kg, and systemic clearance was 2.09+/-0.62 L/kg/h. Transdermal administration of fentanyl resulted in variable plasma concentrations, with peak plasma concentrations ranging from 1.12 to 16.69 ng/ml (mean+/-SD, 6.99+/-6.03 ng/ml) and time to peak concentration ranging from 8 to 18 hours (mean+/-SD, 13+/-4.5 hours). After removal of the transdermal patch, mean+/-SD terminal elimination half-life was 5.34+/-5.34 hours.


CONCLUSIONS
Intravenous administration of fentanyl (2.5 microg/kg) in goats results in a relatively short half-life that will limit its use for management of pain. Transdermal administration of fentanyl (50 microg/h) in goats results in variable plasma concentrations that may exceed those anticipated on the basis of a theoretical delivery rate, but stable plasma concentrations of fentanyl may not be achieved.
Carroll
G L
GL
Department of Small Animal Medicine, College of Veterinary Medicine, Texas A&M University, College Station 77843-4461, USA.
Hooper
R N
RN
Boothe
D M
DM
Hartsfield
S M
SM
Randoll
L A
LA
D000279:Administration, Cutaneous; D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D000818:Animals; D019540:Area Under Curve; D001831:Body Temperature; D018592:Cross-Over Studies; D005260:Female; D005283:Fentanyl / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D006041:Goats / Q000378:metabolism*; D006207:Half-Life; D006339:Heart Rate; D007275:Injections, Intravenous / Q000662:veterinary; D008297:Male; D009716:Numerical Analysis, Computer-Assisted; D011863:Radioimmunoassay / Q000662:veterinary; D012044:Regression Analysis
D000701:Analgesics, Opioid; D005283:Fentanyl