DEVELOPMENT AND USE OF AN ENZYME-LINKED-IMMUNOSORBENT-ASSAY TO MONITOR SERUM AND URINE ACEPROMAZINE CONCENTRATIONS IN THOROUGHBREDS, AND POSSIBLE CHANGES ASSOCIATED WITH EXERCISE

Objectives-To develop an ELISA that is sensitive and suitable for meas urement of immunoreactive acepromazine (ACP) in horse serum and urine and to determine the acute effects of exercise on immunoreactive ACP v alues in Thoroughbreds. Animals-12 healthy Thoroughbreds (5 mares, 5 g eldings, 2 stallions), aged 2 to 8 years. Procedure-A commercially ava ilable antibody and a horseradish peroxidase-conjugated oxime derivati ve of immunoreactive ACP were used to develop a onestep ELISA. Horses were used in a crossover design study to evaluate possible effects of treadmill exercise on serum and urine ACP concentrations after a singl e (25 mg) IM injection of the drug. Results-Immunoreactive ACP was det ectable at concentrations as low as 50 pg/ml in serum and 100 pg/ml in urine, with intra- and interassay variabilities of 1.1 and 5.2%, resp ectively. The antibody had some cross-reactivity with a limited number of other phenothiazines. After drug administration, serum ACP immunor eactivity achieved a peak concentration (10.5 ng/ml) within 30 minutes and could be measured up to 48 hours in serum and 120 hours in urine. Although exercise had no significant effect on serum drug concentrati on, immunoreactive ACP disappeared more quickly (by 48 hours) from the urine of horses in the exercised group. Conclusions-This one-step ELI SA provides a simple and sensitive means to measure immunoreactive ACP in equine serum and urine. The ability to detect drug several days af ter administration of a low dose of ACP should augment efforts to cont rol illicit use of this drug in performance horses. Potential changes in ACP kinetics after exercise warrant further study.