Development and use of an enzyme-linked immunosorbent assay to monitor serum and urine acepromazine concentrations in thoroghbreds, and possible changes associated with exercise.

OBJECTIVES: To develop an ELISA that is sensitive and suitable for measurement of immunoreactive acepromazine (ACP) in horse serum and urine and to determine the acute effects of exercise on immunoreactive ACP values in Thoroughbreds. ANIMALS: 12 healthy Thoroughbreds (5 mares, 5 geldings, 2 stallions), aged 2 to 8 years. PROCEDURE: A commercially available antibody and a horseradish peroxidase-conjugated oxime derivative of immunoreactive ACP were used to develop a one-step ELISA. Horses were used in a crossover design study to evaluate possible effects of treadmill exercise on serum and urine ACP concentrations after a single (25 mg) IM injection of the drug. RESULTS: Immunoreactive ACP was detectable 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%, respectively. The antibody had some cross-reactivity with a limited number of other phenothiazines. After drug administration, serum ACP immunoreactivity 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 concentration, immunoreactive ACP disappeared more quickly (by 48 hours) from the urine of horses in the exercised group. CONCLUSIONS: This one-step ELISA provides a simple and sensitive means to measure immunoreactive ACP in equine serum and urine. The ability to detect drug several days after administration of a low dose of ACP should augment efforts to control illicit use of this drug in performance horses. Potential changes in ACP kinetics after exercise warrant further study.