Pharmacokinetics of fentanyl following intravenous and transdermal administration in horses

L. K. Maxwell, Sara M Thomasy, N. Slovis, C. Kollias-Baker

Research output: Contribution to journalArticlepeer-review

60 Scopus citations


Reasons for performing study: Although fentanyl has been reported to cause CNS excitation in horses, a transdermal therapeutic system (TTS) containing this mu agonist has recently been used empirically in equine medicine to treat moderate to severe pain. A better understanding of the disposition of fentanyl following transdermal administration would facilitate the clinical use of TTS fentanyl to obtain analgesia in horses. Objectives: To determine the pharmacokinetics of fentanyl following i.v. and TTS patch administration in healthy, mature horses and to evaluate the tolerance of horses to TTS fentanyl administration. Methods: The pharmacokinetics of fentanyl in serum were assessed following a single i.v. dose, a single TTS dose, and multiple TTS doses in 6 healthy horses. Physical examinations, haematology and serum biochemistry analyses during transdermal fentanyl application were then performed to determine tolerance of continuous fentanyl administration. Results: Fentanyl was very rapidly and completely absorbed following a single TTS dose. Mean serum fentanyl concentrations consistent with analgesia in other species were reached by 1 h and maintained until 32 h after patch application. Similar steady state serum concentrations were obtained when multiple doses of TTS fentanyl were administered every 48 or 72 h over 8 or 9 days, with less fluctuation in serum concentrations during the 48 h dosing interval. Three horses exhibited brief (<12 h) episodes of increased body temperature; however, transdermal fentanyl administrations were not associated with other significant changes in haematology and biochemistry panels or physical examination findings. Conclusions and potential relevance: Although the pharmacodynamics of fentanyl have not been investigated fully in horses, transdermally-administered fentanyl exhibited a favourable pharmacokinetic profile without clinically relevant side effects and may be a useful analgesic in equine patients.

Original languageEnglish (US)
Pages (from-to)484-490
Number of pages7
JournalEquine Veterinary Journal
Issue number5
StatePublished - Jul 2003


  • Absorption
  • Analgesia
  • Horse
  • Loo-Riegelman
  • Opioids
  • Pharmacokinetics
  • Transdermal

ASJC Scopus subject areas

  • veterinary(all)


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