Pharmacokinetics, clinical efficacy and safety of acetaminophen (paracetamol) in adult horses with naturally occurring chronic lameness.

This study examined the use of acetaminophen in treating long-term lameness in horses. It highlighted that while it provided some temporary improvements, it may not be a lasting solution, but it is safe for the animals with no significant health concerns detected after 21 days of use.

Methods

• The study adopted a longitudinal approach, and subjects consisted of twelve adult horses with a history of chronic lameness.
• These horses were administered acetaminophen orally every twelve hours for twenty-one days at a dose of 30mg/kg.
• Blood samples were then taken from the horses on days seven and twenty-one and analysed for plasma concentrations of acetaminophen using liquid chromatography-tandem mass spectrometry and noncompartmental pharmacokinetic analysis.
• A body-mounted inertial sensor (BMIS) assessed lameness in the horses. Additionally, a ten-point subjective lameness score was also used on the twenty-first day and compared to the untreated baseline evaluation conducted on the thirty-fifth day.
• For complete safety and health evaluations, clinicopathological analysis, hepatic biopsies and gastroscopies were carried out on days negative one and twenty-two.

Results

• The blood analysis from day seven reflected a maximum plasma acetaminophen concentration of 20.83 ± 10.25 μg/mL after approximately 0.40 ± 0.22 hours. On day twenty-one, the concentration dropped to 17.33 ± 6.91 μg/mL, with a time of approximately 0.67 ± 0.26 hours.
• The researchers noted a significant improvement in lameness scores at two and four hours post-treatment. Substantial improvements were also detected in horses with hindlimb lameness at one, two, and eight hours post-therapy.
• There were no significant differences found from the gastroscopy or hepatic biopsy scores between the first and the twenty-second day, indicating the treatment had no adverse effects on the horses over this period.

Conclusions

• The study concluded that while acetaminophen yielded certain transient improvements in lameness in horses, it might not be effective as a standalone therapy.
• It was also highlighted that despite small sample size, multi-limb lameness severity and etiology variability, acetaminophen appeared safe following administration at doses of 30 mg/kg every twelve hours for twenty-one days.
• No clinically significant changes were observed in any of the health evaluations – clinicopathological analysis, hepatic biopsy or gastric ulceration assessments.