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Home / Equine Research Bank / Equine Vet J / Ocular penetration of oral acetaminophen in horses.
Equine veterinary journal2022; 55(5); 899-904; doi: 10.1111/evj.13902

Ocular penetration of oral acetaminophen in horses.

Abstract: Acetaminophen (paracetamol) is increasingly used to treat painful conditions in horses but its ocular penetration has not been studied. Objective: To determine whether orally administered acetaminophen penetrates the aqueous humour of the normal equine eye and report an aqueous humour:serum acetaminophen concentration ratio in horses. Methods: In vivo experiment. Methods: Six privately owned horses with normal ophthalmic examinations weighing 568 ± 65 kg (mean ± standard deviation) and aged 11 ± 4 years were given 20 mg/kg acetaminophen orally every 12 h for a total of six doses. Physical exam parameters were recorded prior to, during, and after the dosing period. One hour after the final dose, horses were sedated and simultaneous aqueous humour and serum samples were collected and analysed for acetaminophen concentrations and selected eicosanoids. An aqueous humour:serum acetaminophen concentration ratio was calculated. A second aqueous humour sample was taken and analysed for eicosanoid concentrations 3 months after acetaminophen dosing. Physical exam data were compared between time points using a mixed model analysis (significance p < 0.05). Results: Acetaminophen was detected in both serum and aqueous humour of all horses and mean ± standard deviation aqueous humour:serum acetaminophen concentration ratio was 44.9 ± 15.9%. No significant changes in physical exam parameters occurred during or after dosing. Eicosanoids were not detected in aqueous humour at any sampling point. Conclusions: Presence of acetaminophen in the aqueous humour may not relate to clinical effect. A therapeutic level of acetaminophen has not been determined in horses, and the absence of ocular inflammation does not reflect conditions in which acetaminophen may be used. Conclusions: Acetaminophen readily penetrates the aqueous humour of the normal equine eye after consecutive oral dosing. Further study is required to determine whether acetaminophen is useful in the treatment of ocular pain and inflammation.
© 2022 The Authors. Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.
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Publication Date: 2022-12-14 PubMed ID: 36482840DOI: 10.1111/evj.13902Google 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.

This study explored whether acetaminophen, often used to manage pain in horses, penetrates the watery fluid (aqueous humour) within the horse’s eye. The research found that orally administered acetaminophen did enter the aqueous humour, but more studies are needed to evaluate its therapeutic value in treating eye pain and inflammation in horses.

Objective and Methods

  • The objective of this research was to assess whether acetaminophen, given orally, penetrates the aqueous humour (a clear fluid in the anterior and posterior chambers of the eye) in horses.
  • The researchers administered six doses of 20mg/kg acetaminophen orally to six healthy horses every 12 hours.
  • Physical examination parameters, including overall health and eye health, of the horses were recorded before, during, and after the medication administration.
  • After the final dose, the horses were sedated and their aqueous humour and serum samples were collected for analysis.
  • The researchers measured the concentration of acetaminophen in the samples and calculated the ratio of aqueous humour to serum acetaminophen concentration.

Results

  • Acetaminophen was detected in the serum and aqueous humour of all the horses.
  • The average concentration ratio of aqueous humour to serum acetaminophen was about 45%.
  • No significant changes were seen in the horses’ physical exam parameters during or after the dosing.

Conclusion

  • The penetration of acetaminophen into the aqueous humour might not be related to its clinical effect. A clinically effective dosage for horses has yet to be established.
  • The absence of inflammation in the eye does not necessarily reflect the conditions under which acetaminophen may be used to treat horses.
  • The study concluded that acetaminophen penetrates the aqueous humour in the equine eye after successive oral dosing, but further investigation is necessary to determine its efficacy in treating ocular pain and inflammation.

Cite This Article

APA
Peraza J, Hector RC, Lee S, Terhaar HM, Knych HK, Wotman KL. (2022). Ocular penetration of oral acetaminophen in horses. Equine Vet J, 55(5), 899-904. https://doi.org/10.1111/evj.13902

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English
Volume: 55
Issue: 5
Pages: 899-904

Researcher Affiliations

Peraza, Jacky
  • Department of Clinical Sciences, Colorado State University, Fort Collins, Colorado, USA.
Hector, Rachel C
  • Department of Clinical Sciences, Colorado State University, Fort Collins, Colorado, USA.
Lee, Sera
  • Department of Clinical Sciences, Colorado State University, Fort Collins, Colorado, USA.
Terhaar, Hannah M
  • Department of Clinical Sciences, Colorado State University, Fort Collins, Colorado, USA.
Knych, Heather K
  • Department of Clinical Sciences, Colorado State University, Fort Collins, Colorado, USA.
Wotman, Kathryn L
  • Department of Clinical Sciences, Colorado State University, Fort Collins, Colorado, USA.

MeSH Terms

  • Horses
  • Animals
  • Acetaminophen
  • Inflammation / veterinary
  • Horse Diseases / drug therapy

Grant Funding

  • Colorado State University Young Investigator Grant

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Citations

This article has been cited 2 times.
  1. Mercer MA, Davis JL, McKenzie HC. The Clinical Pharmacology and Therapeutic Evaluation of Non-Steroidal Anti-Inflammatory Drugs in Adult Horses. Animals (Basel) 2023 May 10;13(10).
    doi: 10.3390/ani13101597pubmed: 37238029google scholar: lookup
  2. Dagenais A, Juette T, Benoit-Biancamano MO, Vanore M. Reducing Recurrence in Equine Corneolimbal SCC: Outcomes of Adjunctive Cisplatin Biodegradable Bead Therapy. Vet Sci 2026 Jan 12;13(1).
    doi: 10.3390/vetsci13010076pubmed: 41600732google scholar: lookup
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