Philip Moses, Karakka Kal Abdul Khader, Subhahar Michael Benedict, Karatt Tajudheen K, Mathew Binoy, Perwad Zubair, Graiban Fatma Mohammed, Caveney Marina Rodriguez, Sayed Ramy, Kadry Ahmed Mahmoud
Equine Forensic Unit, Central Veterinary Research Laboratory, Dubai, United Arab Emirates.
Rapid Commun Mass Spectrom. 2023 Feb 15;37(3):e9430. doi: 10.1002/rcm.9430.
According to previous research, aminorex is the major metabolite of levamisole; however, in the screening of levamisole-positive racehorse urine and plasma samples, aminorex could only be detected in trace amounts or not at all. In forensic laboratories, hydroxy levamisole and its phase II conjugates make it easier to confirm levamisole misuse and to differentiate between the abuse of levamisole and aminorex. This study aimed to identify the major levamisole metabolites that can be detected along with the parent drug.
The study describes levamisole and its metabolites in thoroughbred horses following oral administration and in vitro with equine liver microsomes. The plausible structures of the detected metabolites were postulated using liquid chromatography combined with high-resolution mass spectrometry.
Under the experimental conditions 26 metabolites (17 phase I, 2 phase II, and 7 conjugates of phase I metabolites) were detected (M1-M26). The major phase I metabolites identified were formed by hydroxylation. In phase II, the glucuronic acid conjugates of levamisole and hydroxy levamisole were detected as the major metabolites. In plasma, the parent drug and major metabolites are detectable for up to eight days, while in urine, they are detectable for up to twenty days. Levamisole levels rapidly increased at 45 min following administration, then declined gradually until detectable levels were reached approximately 8 days after administration, according to a pharmacokinetics study.
A prolonged elimination profile and relatively high concentration of hydroxy metabolites suggest that the detection of hydroxy metabolites is imperative for investigating levamisole doping in horses.
根据先前的研究，氨基雷司是左旋咪唑的主要代谢产物；然而，在对左旋咪唑阳性赛马尿液和血浆样本的筛查中，只能检测到痕量的氨基雷司或根本检测不到。在法医实验室中，羟基左旋咪唑及其Ⅱ相缀合物更易于确认左旋咪唑的滥用情况，并区分左旋咪唑和氨基雷司的滥用。本研究旨在鉴定可与母体药物一起检测到的主要左旋咪唑代谢产物。
该研究描述了纯种马口服给药后以及在体外与马肝微粒体共同作用下左旋咪唑及其代谢产物的情况。利用液相色谱结合高分辨率质谱推测所检测到的代谢产物的可能结构。
在实验条件下，检测到了26种代谢产物（17种Ⅰ相代谢产物、2种Ⅱ相代谢产物以及7种Ⅰ相代谢产物的缀合物）（M1 - M26）。鉴定出的主要Ⅰ相代谢产物是通过羟基化形成的。在Ⅱ相中，左旋咪唑和羟基左旋咪唑的葡萄糖醛酸缀合物被检测为主要代谢产物。在血浆中，母体药物和主要代谢产物在长达8天的时间内均可检测到，而在尿液中，它们在长达20天的时间内均可检测到。根据一项药代动力学研究，给药后45分钟时左旋咪唑水平迅速升高，然后逐渐下降，直到给药后约8天达到可检测水平。
消除曲线延长以及羟基代谢产物浓度相对较高表明，检测羟基代谢产物对于调查马匹中的左旋咪唑兴奋剂使用情况至关重要。
