Pilot study to quantify the time to clear dexamethasone from plasma and urine of adult horses following a single nebulisation.

This study sought to determine the length of time it takes for horses to clear dexamethasone from their systems, particularly from the blood and urine, after being administered a single dose via nebulisation.

Research Methodology

The research adopted an experimental design in which:

• Six Standardbred mares (female horses) were utilized for the study.
• A single dose of Dexamethasone sodium phosphate (0.04 mg/kg) diluted in 0.9% sodium chloride was administered to each horse using a Flexineb E2® nebuliser.
• At several points in time (from 0 to 96 hours post-nebulisation), blood and urine samples were drawn from each horse and analysed.
• A technique called liquid chromatography mass spectrometry, a highly sensitive and reliable method for detecting substances in biological samples, was used for this analysis.

Research Findings

The results from the research study were as follows:

• Maximum plasma concentrations of dexamethasone were reached by the earliest detection point (2 hours) after nebulisation, with concentrations ranging from 0.6 to 1.8 ng/mL. After 48 hours, the substance was undetectable in the plasma. Notwithstanding, in one horse, a trace level (0.1 ng/mL) was detected at 96 hours following three consecutive readings of 0 ng/mL.
• The urine samples appeared to clear the dexamethasone faster, with maximum concentrations reached by the earliest collection point (1 hour) after nebulisation. The concentrations ranged from 3.2 to 23.8 ng/mL. At 72 hours post-nebulisation, five of the horses had completely cleared the dexamethasone from their urine, but for one horse, a trace level (0.1 ng/mL) was still present at 96 hours.

Conclusion

Conclusively, this research showed that:

• A single dose of 0.04 mg/kg of dexamethasone administered as an aerosol through a FlexinebE2® mask was no longer detectable in the blood at 48 hours. However, for one horse the dexamethasone was detectable (though minimal) even at 96 hours post-nebulisation.
• From the urine samples, it was concluded that dexamethasone was not identifiable 72 hours post-nebulisation in five horses, but in one horse, a low concentration (0.1 ng/mL) was still present at 96 hours.

This study provides crucial data about the pharmacokinetics of dexamethasone in horses, and might have significant implications for equine care and doping control in horse sports.