Elimination of cetirizine following administration of multiple doses to exercised thoroughbred horses.

The research observed the rate at which the drug Cetirizine, an antihistamine administered for hypersensitivity reactions, is eliminated from the bodies of exercised thoroughbred horses. Results showed that after the final dose, the average serum Cetirizine concentrations were above the Lowest Observed Adverse Effect Level even 48 hours after administration.

Research Purpose and Methodology

• The main goal of this study was to understand the disposition and elimination of Cetirizine after being administered orally. This is important in establishing regulatory guidelines for the use of the drug, particularly in relation to competition horses as it’s necessary to have a withdrawal time for the medication prior to a race.
• The research involved nine thoroughbred horses that were given routine exercise. These horses were each given a dose of 0.4 mg of Cetirizine twice a day (once every 12 hours), for a total of five doses.
• Blood samples were obtained from each horse before administering the drug and at multiple time points after administration. These blood samples were then analyzed to measure the concentration of Cetirizine in the serum.

Findings and Conclusion

• The primary metric analyzed in this study was the serum elimination half-life of Cetirizine, which was found to be approximately 5.83 hours. This indicates the time required for the drug concentration to reduce by half in the horse’s bloodstream.
• Another notable conclusion from the study was that 48 hours after administering the final dose, the average concentration of Cetirizine in the serum was still higher than the Lowest Observed Adverse Effect Level (LOAEL). The LOAEL refers to the minimum concentration of the medication that can cause an adverse effect. It was concluded that even after two days of the final dose, residual quantities of the drug were still present in the horse’s body, implying a longer withdrawal time may be needed before the horses can compete.
• The findings from this study are essential in providing supplementary data required to devise appropriate regulations around the use of Cetirizine in performance horses, which will aid in ensuring their safety and welfare.