L- and D-threo ethylphenidate concentrations, pharmacokinetics, and pharmacodynamics in horses.

This research investigates the concentrations, pharmacokinetics, and pharmacodynamics of two forms of the psychostimulant Ethylphenidate in horses. With the primary goals of understanding the drug’s effects and establish a method to control its misuse in equine athletes, trials were carried out in three dose groups to monitor the impact and understand the metabolism process of the given drug.

Methods and Procedures

• Twelve horses were selected and randomized into three groups: Each group received different doses of Ethylphenidate (intravenous: 10 mg or 40 mg, oral: 40 mg).
• The research team collected blood and urine samples from the horses before and up to 72 hours after Ethylphenidate administration.
• The team then measured the concentrations of D-threo Ethylphenidate and its metabolite, Ritalinic acid, using a method known as Liquid Chromatography-tandem Mass Spectrometry.
• The L-threo Ethylphenidate concentrations were estimated based on the D-threo Ethylphenidate concentrations observed.

Results

• Serum concentrations of Ethylphenidate were below detectable levels by 8, 18, and 12 hours following intravenous administration of 10 mg and 40 mg and oral administration of 40 mg, respectively.
• Interestingly, Ritalinic acid, the metabolite of Ethylphenidate, was non-detectable at 72 hours in the group that received a 10-mg intravenous and 40-mg oral dose of Ethylphenidate.
• The study also highlighted Ritalinic acid concentrations being below detectable levels 72 hours after an intravenous administration of 40 mg of Ethylphenidate.

Observations and Findings

• Despite the small number of horses in each dose group, the study noted neither stimulatory behavior nor significant changes in the heart rate of the horses.
• However, adverse gastrointestinal effects were observed in all the groups, pointing out possible negative side effects of the drug on horses.

Conclusion

• This study provides vital information about how Ethylphenidate is processed in horses. Understanding the time taken to metabolize and expel Ethylphenidate from their system is important for regulating the use of this drug in equine athletes.
• Although no stimulatory behavior was observed, the gastrointestinal effects require further investigation to gauge the safety of the drug in horses.