Pemoline

Abstract: The number of potentially abused substances in horse racing is very large and it is not easy to analyze the full range.To facilitate the analyses of substances of abuse, a method has been developed for 63 substances in horse urine using liquid chromatog.-tandem mass spectrometry.The developed method has been validated according to the 2021/808/EC and AORC criteria.The horse urine samples were extracted after enzymic hydrolysis via a C8-BCX SPE cartridge with an automated SPE and analyzed by LC-MS/MS.According to the validation study results, the within-laboratory reproducibility CV was no more than 13.9% and the average recoveries ranged from 90.71 to 117.94% for repeatability and reproducibility.The decision limits (CCα) for quant. anal. and detection capabilities (CCβ) for qual. screening were close to the targeted limit for each substance.The results of the present study showed that the method was able to perform quant. analyses of 54 substances and screening analyses of 9 substances (total 63) in horse urine and that the results were valid and applicable.The validated method was successfully applied to five proficiency tests and three suspected samples.

Levamisole is a regulated substance sometimes administered to racehorses to treat equine protozoal myelitis. Metabolites include compound II, aminorex, and pemoline. Aminorex and pemoline are Horseracing Integrity and Safety Authority–banned substances. Previous studies have examined single doses of the drug. This study examined the disposition of levamisole after 7 days of dosing.

6 healthy Thoroughbred geldings.

Horses were treated with 500 mg (approx 0.91 to 1 mg/kg) of compounded levamisole hydrochloride paste PO every 12 hours for a total of 13 doses over 7 days. Serum and urine samples were analyzed for levamisole and its metabolites over a 28-day period.

The terminal half-life of levamisole in serum was variable between horses. Following the last dose of levamisole on day 7, serum levamisole levels took 3 to 14 days (days 10 to 21) to fall below the limit of detection (LOD) in 5 of 6 horses. Serum from 1 horse remained over LOD on the last testing day (day 28). In urine, following the final dose (day 7), levamisole was below LOD on day 13 (6 days after final dose) and aminorex was below LOD on day 10 (3 days after final dose). Compound II was above LOD in 4 of 5 horses sampled on the last sampling day (day 28).

Levamisole and its metabolites can be detected for variable lengths of time in horses, with detection lasting for days to weeks following multiple doses. This study supports the Racing Medication and Testing Consortium Advisory on levamisole, which suggests that clearance sample testing should be conducted on treated horses to verify elimination of levamisole and its metabolites.