1Maxwell H. Gluck Equine Research Center, Martin-Gatton College of Agriculture, Food and Environment, University of Kentucky, Lexington, KY.
2Racing Medication and Testing Consortium, Lexington, KY.
J Am Vet Med Assoc. 2024 Sep 13;262(12):1632-1638. doi: 10.2460/javma.23.06.0340. Print 2024 Dec 1.
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.
左旋咪唑是一种受管制的物质，有时用于治疗马的原虫性脊髓炎。其代谢物包括化合物 II、氨苯砜和苯丙胺。氨苯砜和苯丙胺均被 Horseracing Integrity and Safety Authority 列为禁用物质。此前的研究检查了单次给药的情况。本研究检查了连续给药 7 天后左旋咪唑的处置情况。
6 匹健康的纯血马公马。
马匹每天接受 500mg（约 0.91 至 1mg/kg）的复方盐酸左旋咪唑膏剂，每天 2 次，共 13 次，7 天内完成。在 28 天内分析血清和尿液中的左旋咪唑及其代谢物。
6 匹马的血清中左旋咪唑的终末半衰期各不相同。在第 7 天最后一次给药后，5 匹马的血清左旋咪唑水平在第 10 至 21 天（第 13 至 21 天）降至 5 匹马中的 3 匹马的检测限（LOD）以下，第 1 匹马的血清直至最后检测日（第 28 天）仍高于 LOD。尿液中，末次给药（第 7 天）后，左旋咪唑在第 13 天（末次给药后 6 天）低于 LOD，氨苯砜在第 10 天（末次给药后 3 天）低于 LOD。化合物 II 在最后采样日（第 28 天）的 4 匹采样马中仍高于 LOD。
马匹中左旋咪唑及其代谢物的检测时间长短不一，连续给药后可检测数天至数周。本研究支持 Racing Medication and Testing Consortium Advisory 对左旋咪唑的建议，即应在接受治疗的马匹中进行清除样本检测，以确认左旋咪唑及其代谢物已被清除。
