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Journal of veterinary pharmacology and therapeutics2021; 45(2); 188-195; doi: 10.1111/jvp.13041

Pharmacokinetics of diphenhydramine following single-dose intravenous and oral administration in non-fasted adult horses.

Abstract: Diphenhydramine is an H1 receptor antagonist used to control urticaria and other allergic signs caused by type I hypersensitivity reactions in horses (Equus caballus). Limited studies have been conducted on pharmacokinetics of this drug in horses, with no studies involving oral formulations. Our study investigated pharmacokinetics of an oral diphenhydramine formulation compared to intravenous administration in non-fasted adult horses. Six healthy horses underwent a single administration of three different doses of diphenhydramine (1 mg/kg intravenously, 1 mg/kg intragastrically, and 5 mg/kg intragastrically) with a two-week washout period between doses. Bioavailability of intragastric diphenhydramine was less than one percent and six percent for 1 mg/kg and 5 mg/kg intragastric doses, respectively. This poor bioavailability is similar to what is reported in dogs. Two of six horses experienced transient side effects after intravenous diphenhydramine administration, emphasizing the need for determining therapeutic plasma levels in efforts to determine the lowest effective dose minimizing risk of adverse effects. The main conclusion of our study was that oral diphenhydramine at doses up to 5 mg/kg are unlikely to achieve therapeutic plasma levels in adult horses.
Publication Date: 2021-12-17 PubMed ID: 34921427DOI: 10.1111/jvp.13041Google Scholar: Lookup
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  • Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The research study focuses on the effectiveness of diphenhydramine, an antihistamine medication, when it’s administered intravenously and orally to adult horses. The results suggest that oral administration of the drug is much less effective, pointing to a need for further studies to establish the most efficient dosage and method of administering the drug that minimizes side effects.

Research Methodology

  • The study involved six healthy adult horses. These horses were not fasted before the administration of diphenhydramine.
  • Three different doses of diphenhydramine were administered: 1 mg/kg intravenously, 1 mg/kg intragastrically (through the stomach), and 5 mg/kg intragastrically.
  • A period of two weeks was given between each dose for a thorough washout, ensuring that any residual effects from the previous doses were eliminated.

Findings

  • The oral bioavailability of diphenhydramine at each dose was found to be less than one percent and six percent for the 1 mg/kg and 5 mg/kg intragastric doses, respectively, suggesting that the oral route is inefficient for absorption of diphenhydramine in horses.
  • The low bioavailability observed in this study is similar to that reported in earlier studies in dogs.
  • Two of the six horses subjected to intravenous administration showed transient side effects indicating that careful attention needs to be paid to dosing to minimize adverse reactions.

Conclusion

  • The significant finding of the research was that oral dosing of diphenhydramine at doses up to 5 mg/kg is unlikely to result in therapeutic plasma levels in adult horses. This implies that alternative routes of administration or higher doses may be needed to achieve therapeutic effects.
  • There is a need for further research to establish the most effective dosage and mode of administration for diphenhydramine in adult horses while minimizing side effects.

Cite This Article

APA
Redmond JS, Stang BV, Schlipf JW, Christensen JM. (2021). Pharmacokinetics of diphenhydramine following single-dose intravenous and oral administration in non-fasted adult horses. J Vet Pharmacol Ther, 45(2), 188-195. https://doi.org/10.1111/jvp.13041

Publication

ISSN: 1365-2885
NlmUniqueID: 7910920
Country: England
Language: English
Volume: 45
Issue: 2
Pages: 188-195

Researcher Affiliations

Redmond, Jeremy S
  • Department of Clinical Sciences, Carlson College of Veterinary Medicine, Oregon State University, Corvallis, Oregon, USA.
Stang, Bernadette V
  • Department of Clinical Sciences, Carlson College of Veterinary Medicine, Oregon State University, Corvallis, Oregon, USA.
Schlipf, John W
  • Department of Clinical Sciences, Carlson College of Veterinary Medicine, Oregon State University, Corvallis, Oregon, USA.
Christensen, John M
  • College of Pharmacy, Oregon State University, Corvallis, Oregon, USA.

MeSH Terms

  • Administration, Intravenous / veterinary
  • Administration, Oral
  • Animals
  • Biological Availability
  • Cross-Over Studies
  • Diphenhydramine
  • Dogs
  • Histamine H1 Antagonists
  • Horses

Grant Funding

  • Oregon State University

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