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Article

Pharmacokinetic Profile of Fentanyl in the Koala (Phascolarctos cinereus) after Intravenous Administration, and Absorption via a Transdermal Patch

1
Currumbin Wildlife Hospital, Currumbin, Gold Coast 4223, Australia
2
Sydney School of Veterinary Science, The University of Sydney, Camperdown, Sydney 2006, Australia
*
Author to whom correspondence should be addressed.
Academic Editor: Natasha Speight
Animals 2021, 11(12), 3550; https://doi.org/10.3390/ani11123550
Received: 21 November 2021 / Revised: 9 December 2021 / Accepted: 10 December 2021 / Published: 14 December 2021
(This article belongs to the Special Issue Health and Diseases of Koalas)
Koalas can be injured by cars and bushfires, and be affected by painful infectious diseases. When koalas undergo surgery to repair broken bones, they require analgesia. Fentanyl is a potent opioid that can be administered during surgery to provide analgesia. This study describes the rate of elimination of fentanyl in koalas’ blood when administered as a single intravenous injection and consequently calculates the dose rate to administer a constant rate fentanyl infusion into the koalas’ veins to provide short-term pain control. Fentanyl can also be absorbed via the skin into the circulation when applied as a transdermal patch. Although the data for transdermal fentanyl patch absorption is from two koalas only, the results demonstrate that when a patch is applied, pain control is likely to occur 12 h after application to koalas’ skin. Fentanyl may provide effective pain control to koalas either as an intravenous infusion or as a transdermal patch.
Fentanyl was administered as a single intravenous bolus injection at 5 µg/kg to five koalas and fentanyl plasma concentrations for a minimum of 2 h were quantified by an enzyme-linked immunosorbent assay (ELISA). The median (range) fentanyl elimination half-life and clearance were 0.53 (0.38–0.91) h, and 10.01 (7.03–11.69) L/kg/h, respectively. Assuming an analgesic therapeutic plasma concentration of 0.23 ng/mL (extrapolated from human studies), an intravenous constant infusion rate was estimated at approximately between 1.7 to 2.7 µg/kg/h (using the clearance 95% confidence intervals). A transdermal fentanyl patch was applied to the antebrachium of an additional two koalas for 72 h. Fentanyl plasma concentrations were determined during the patch application and after patch removal at 80 h. The fentanyl plasma concentration was greater than 0.23 ng/mL after 12 to 16 h. While the patch was applied, the maximum fentanyl concentration was approximately 0.7 ng/mL from 32 to 72 h. Fentanyl plasma concentrations increased to 0.89 ng/mL 1 h after the patch was removed, and then decreased to a mean of 0.47 ng/mL at 80 h. The transdermal fentanyl patch is likely to provide some level of analgesia but should be initially co-administered with another faster acting analgesic for the first 12 h. View Full-Text
Keywords: fentanyl; koala; Phascolarctos cinereus; transdermal patch; analgesia; opioid fentanyl; koala; Phascolarctos cinereus; transdermal patch; analgesia; opioid
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MDPI and ACS Style

Tokonami, F.; Kimble, B.; Govendir, M. Pharmacokinetic Profile of Fentanyl in the Koala (Phascolarctos cinereus) after Intravenous Administration, and Absorption via a Transdermal Patch. Animals 2021, 11, 3550. https://doi.org/10.3390/ani11123550

AMA Style

Tokonami F, Kimble B, Govendir M. Pharmacokinetic Profile of Fentanyl in the Koala (Phascolarctos cinereus) after Intravenous Administration, and Absorption via a Transdermal Patch. Animals. 2021; 11(12):3550. https://doi.org/10.3390/ani11123550

Chicago/Turabian Style

Tokonami, Fumie, Benjamin Kimble, and Merran Govendir. 2021. "Pharmacokinetic Profile of Fentanyl in the Koala (Phascolarctos cinereus) after Intravenous Administration, and Absorption via a Transdermal Patch" Animals 11, no. 12: 3550. https://doi.org/10.3390/ani11123550

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