Pharmacokinetics of Ethyl Glucuronide and Ethyl Sulfate and Pharmacodynamic Effects Following Intravenous and Oral Administration of Ethanol to Exercised Horses

Ethanol, a central nervous system depressant and banned substance in horseracing, has reportedly been administered to horses prior to competition to "calm a horse's nerves." In this study, the pharmacokinetics of two metabolites of ethanol were studied to better understand the behavior of this compound in the horse and provide a scientific basis for regulation of its administration. Six horses received a single intravenous (30 mL; 1200 mg) and oral (90 mL; 3600 mg) administration of ethanol (vodka, 40% ABV) in a balanced cross-over design. Blood and urine samples were collected at various times post administration for up to 24 h. Concentrations of ethyl glucuronide and ethyl sulfate were determined using liquid chromatography-tandem mass spectrometry and pharmacokinetic analysis performed. Behavioral, locomotor activity and effects on heart rate were assessed. The maximum concentration (mean ± SD) of ethyl glucuronide was 71.5 ± 42.7 and 105.0 ± 47.5 ng/mL at 0.88 h following IV and oral administration, respectively. The maximum concentrations for the ethyl sulfate metabolite following IV and oral administration were 1.61 ± 0.60 and 3.46 ± 1.68 ng/mL, respectively. Urine concentrations of both metabolites were non-detectable by 24 h post ethyl alcohol administration. No observable behavioral responses were noted following IV or oral administration. Significant decreases in heart rate were noted at various times starting at 10 min until 4 h post administration in the oral dose group. Both ethyl glucuronide and ethyl sulfate could be useful markers for detection of illicit administration of ethanol to horses.