Pharmacokinetics of fentanyl after intravenous and transdermal administration in goats

Gwendolyn L. Carroll From the Departments of Small Animal Medicine and Surgery (Carroll, Hartsfield, Randoll), Large Animal Medicine and Surgery (Hooper), and Physiology and Pharmacology (Boothe), College of Veterinary Medicine, Texas A&M University, College Station, TX 77843-4461.

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R. Neil Hooper From the Departments of Small Animal Medicine and Surgery (Carroll, Hartsfield, Randoll), Large Animal Medicine and Surgery (Hooper), and Physiology and Pharmacology (Boothe), College of Veterinary Medicine, Texas A&M University, College Station, TX 77843-4461.

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Dawn M. Boothe From the Departments of Small Animal Medicine and Surgery (Carroll, Hartsfield, Randoll), Large Animal Medicine and Surgery (Hooper), and Physiology and Pharmacology (Boothe), College of Veterinary Medicine, Texas A&M University, College Station, TX 77843-4461.

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Sandee M. Hartsfield From the Departments of Small Animal Medicine and Surgery (Carroll, Hartsfield, Randoll), Large Animal Medicine and Surgery (Hooper), and Physiology and Pharmacology (Boothe), College of Veterinary Medicine, Texas A&M University, College Station, TX 77843-4461.

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Lynne A. Randoll From the Departments of Small Animal Medicine and Surgery (Carroll, Hartsfield, Randoll), Large Animal Medicine and Surgery (Hooper), and Physiology and Pharmacology (Boothe), College of Veterinary Medicine, Texas A&M University, College Station, TX 77843-4461.

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Abstract

Objective

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

Animals

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

Procedure

Each goat was given 2 treatments consisting of fentanyl administered IV (2.5 μg/kg of body weight) and via a transdermal patch (50 μg/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 and Clinical Relevance

Intravenous administration of fentanyl (2.5 μg/kg) in goats results in a relatively short half-life that will limit its use for management of pain. Transdermal administration of fentanyl (50 μg/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. (Am J Vet Res 1999;60:986–991)

Abstract

Objective

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

Animals

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

Procedure

Each goat was given 2 treatments consisting of fentanyl administered IV (2.5 μg/kg of body weight) and via a transdermal patch (50 μg/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 and Clinical Relevance

Intravenous administration of fentanyl (2.5 μg/kg) in goats results in a relatively short half-life that will limit its use for management of pain. Transdermal administration of fentanyl (50 μg/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. (Am J Vet Res 1999;60:986–991)

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