Use of enzyme-linked immunosorbent assay and radioimmunoassay to determine serum and urine dexamethasone concentrations in thoroughbreds after intravenous administration of the steroid.

OBJECTIVE

To develop a simple and sensitive ELISA for detection of dexamethasone in horse serum and urine.

SAMPLE POPULATION

Blood and urine samples from 3 thoroughbred mares.

PROCEDURE

A dexamethasone oxime was prepared and conjugated to hemocyanin, bovine serum albumin and to horseradish peroxidase. One- and two-step double-antibody ELISA methods, as well as a radioimmunoassay method, were performed. The one-step ELISA was used to test urine from 3 Thoroughbred mares injected with 5 mg of dexamethasone, IV.

RESULTS

The ELISA could detect dexamethasone in the range of 0.01 to 50 ng/ml, with intra- and interassay variations of 8.92 and 9.42%, respectively. Serum dexamethasone concentration reached a peak of 20 to 35 ng/ml 15 minutes after steroid administration and decreased to 1 ng/ml in 2.5 hours. Urine dexamethasone concentration 18 to 50 ng/ml 1 to 2 hours after drug administration and decreased to 1 ng/ml at 10 hours.

CONCLUSION

The developed assay is sensitive as well as simple for detecting dexamethasone in horse serum and urine, and is comparable to radioimmunoassay.

CLINICAL RELEVANCE

This method can be useful for screening samples from racehorses, because it is sensitive and does not require sample preparation or sophisticated equipment.