Establishing the cut-off concentration for the detection of etorphine in horse urine.

This study outlines the application of a 125I radioimmunoassay to identify the patterns of excretion in horse urine following the administration of varying doses of etorphine. The findings suggest that radioimmunoassay could be a valuable early-stage method in detecting etorphine use in racing horses.

Methods of the research

• The researchers used a 125I radioimmunoassay to study the pattern of urinary excretion of etorphine, a potent semi-synthetic opiate.
• Three thoroughbred horses were used for the experiment. Each horse was given various doses of etorphine (5, 15, 30, and 100 micrograms) via intramuscular injection.
• Urine samples were collected from the horses for up to 72 hours post-injection.
• Additionally, 48 urine samples were collected from horses who hadn’t received etorphine.

Findings of the research

• Findings showed that the maximum concentration of etorphine following a 5-microgram dose was 711 pg ml-1, while a 15-microgram dose led to 2661 pg ml-1, a 30 micrograms dose resulted in 3344 pg ml-1, and a 100-microgram dose gave more than 10,000 pg ml-1.
• The concentration of etorphine remained above 100 pg ml-1 for varying amounts of time based on the dosage amount.
• In all 48 samples from horses not given etorphine, the concentration levels were below 100 pg ml-1.
• No significant increase in etorphine concentrations was observed after hydrolysis of samples with beta-glucuronidase and aryl sulfatase.
• The half-lives of etorphine, as calculated for the 100 microgram dose, differed among the three horses, being 569, 803, and 821 minutes, respectively.

Conclusion of the research

• The researchers concluded that radioimmunoassay can provide a useful preliminary method for evaluating the use of etorphine in racing horses. The effectiveness of this approach is indicated by its ability to detect varying etorphine levels in horse urine, based on the administered dosage.