Methadone screening of racehorses.

The misuse of opiates in racehorses relates to their effect of increasing locomotor activity. Because methadone, a narcotic analgesic, has been suspected of use as a doping compound in the past, it was added to the list of banned drugs and should be considered in doping control. Because the literature fails to provide information on detection of methadone in blood or urine of horses, an enzyme-linked immunosorbent assay was developed to monitor this narcotic in equine body fluids. Combined with high-performance liquid chromatography, the immunoassay also served to confirm positives indicated by screening. Following intravenous administration of methadone (0.1 mg/kg), the drug was found for up to 24 h in blood but was never identified in urine (10-pg/mL detection limit). Thus, urine is dismissed as a source of methadone control, and the use of blood to screen racehorses for this narcotic analgesic is suggested.