Ocular penetration of oral acetaminophen in horses.
Authors: Peraza Jacky, Hector Rachel C, Lee Sera, Terhaar Hannah M, Knych Heather K, Wotman Kathryn L
Journal: Equine veterinary journal
Summary
# Editorial Summary: Ocular penetration of oral acetaminophen in horses Acetaminophen (paracetamol) is gaining popularity in equine pain management, yet its ability to reach ocular tissues—crucial for treating eye-related discomfort—remained unexplored until this 2023 investigation. The researchers administered 20 mg/kg acetaminophen orally every 12 hours to six healthy horses over three days, then collected simultaneous serum and aqueous humour samples one hour after the final dose to measure drug penetration and analyse inflammatory markers. All horses achieved detectable acetaminophen levels in the aqueous humour, with a mean aqueous humour:serum concentration ratio of 44.9%, and notably, no physical examination changes or inflammatory eicosanoids were observed during treatment or at three-month follow-up. Whilst the data confirms that orally dosed acetaminophen does penetrate the eye, the clinical significance remains unclear: the study was conducted in healthy, pain-free horses without ocular inflammation, so the therapeutic benefit in actual cases of eye pain or uveitis cannot yet be assumed. Practitioners should recognise that drug presence does not automatically equate to clinical efficacy, and further research in naturally inflamed or painful eyes is essential before confidently recommending acetaminophen as a first-line treatment for equine ocular conditions.
Read the full abstract on PubMed
Practical Takeaways
- •Orally administered acetaminophen does penetrate the equine eye, but clinical significance for treating ocular pain remains unproven in normal eyes
- •No adverse ophthalmic effects were observed in this small study, but therapeutic efficacy and safety for ocular conditions require further investigation
- •Current evidence does not support recommending acetaminophen specifically for equine ocular pain or inflammation until therapeutic levels are established and clinical benefit demonstrated
Key Findings
- •Acetaminophen was detected in aqueous humour of all 6 horses after oral dosing at 20 mg/kg every 12 hours for 6 doses
- •Mean aqueous humour:serum acetaminophen concentration ratio was 44.9 ± 15.9%, indicating substantial ocular penetration
- •No significant changes in physical examination parameters occurred during or after acetaminophen dosing
- •Eicosanoids were not detected in aqueous humour at any sampling point, suggesting no inflammatory response in normal eyes