Development of a method for the detection and confirmation of the alpha-2 agonist amitraz and its major metabolite in horse urine.

The research article focuses on the development of a detection method for Amitraz, a sedative veterinary drug, and its major metabolite in horse urine. Historically, Amitraz’s potential to influence horse races led to its classification as a Class 3 Foreign Substance. The study presents a sensitive gas chromatographic-mass spectrometric (GC-MS) method to accurately, rapidly, and confidently detect its presence in performance horses.

Methodology

• The researchers determined the main equine metabolite of Amitraz through electrospray ionization(+)-mass spectrometry, naming it as N-2,4-dimethylphenyl-N’-methylformamidine.
• A gas chromatographic-mass spectrometric (GC-MS) method was then developed to detect, quantify, and confirm this metabolite in performance horse regulation. GC-MS is a method that combines the features of gas-liquid chromatography and mass spectrometry to identify different substances within a test sample.
• This useful process involved treating the sample with tert-butyldimethylsilyl groups, which are used for protection in organic chemistry, to prepare it for analysis.

Analytical approach

• The approach involved selected ion monitoring (SIM) of certain ion levels associated with the presence of the metabolite – m/z 205, 278, 261, and 219.
• A calibration curve, which is a graph of the response of an analytical instrumentation relative to the amount of substance in the sample, was plotted based on the observed ion area ratios. This step is crucial to enable quantitation of the metabolite concentration.
• The detection method simultaneously incorporated an internal standard for the quantifier ion based on a specialized synthesized compound, a d(6) deuterated metabolite, which helps in providing a reliable measurement by compensating for any variations in the analytical setup.

Test and Results

• The sensitivity of this developed method allows detection down to 5 ng/mL levels of Amitraz’s principal metabolite in horse urine.
• This is precise enough to recognize the peak urinary metabolite presence at just about 1 hour after dosage, following the administration of Amitraz at a high 75-mg per horse intravenous dose.

Overall, the research presents a solid analytical approach that not only identifies but also quantifies the monitored substance, providing crucial information for racing regulation and oversight.